Flexible circuit board, COF module and electronic device comprising the same

ABSTRACT

A flexible circuit board and an electronic device including a flexible circuit board are provided. The flexible circuit board may include a substrate having a bending area and a non-bending area, a wiring pattern layer provided on the bending area and the non-bending area, a plating layer provided on the wiring pattern layer and including an open area in an area corresponding to the bending area, and a protective layer that directly contacts one surface of the wiring pattern layer exposed at the open area and a side surface of the plating layer. The protective layer may have a larger thickness than a thickness of the plating layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of prior U.S. patentapplication Ser. No. 15/657,296 filed Jul. 24, 2017, which claimspriority under 35 U.S.C. § 119 to Korean Application No.10-2016-0093748, filed on Jul. 22, 2016, and Korean Patent ApplicationNo. 10-2016-0102902, filed on Aug. 12, 2016, whose entire disclosuresare incorporated herein by reference

BACKGROUND 1. Field

A flexible circuit board, a chip on film (COF) module, and an electronicdevice including a flexible circuit board and a COF module are provided.

2. Background

Various electronic products are becoming thinner, miniaturized, andlighter. Research for mounting semiconductor chips with high density ina narrow region of an electronic device is being conducted in variousways. For example, since a chip on film (COF) method uses a flexiblesubstrate, the COF method may be applied to both a flat panel displayand a flexible display. Since the COF method may be applied to variouselectronic devices, the COF method is attracting attention. Since theCOF method may have a fine pitch, the COF method may be used for ahigh-resolution display as pixelation increases.

A chip on film (COF) method is a method in which a semiconductor chipmay be mounted on a flexible circuit board in the form of a thin film.For example, the semiconductor chip may be an integrated circuit (IC)chip or a large scale integrated circuit (LSI) chip. However, in a COFflexible circuit board, a crack may be generated in the process ofrepeatedly bending a circuit pattern formed on a flexible substrate orbonding in a bent state, and the COF flexible circuit board may bedamaged by a tensile force generated during bending.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments will be described in detail with reference to thefollowing drawings in which like reference numerals refer to likeelements wherein:

FIG. 1 to FIG. 4 are various cross-sectional views of a flexible circuitboard according to an embodiment;

FIG. 5 to FIG. 8 are various cross-sectional views of a double-sidedflexible printed circuit board according to an embodiment;

FIG. 9 to FIG. 12 are cross-sectional views of a manufacturing processof the double-sided flexible printed circuit board;

FIG. 13 to FIG. 20 are various cross-sectional views of a flexiblecircuit board according to another embodiment;

FIG. 21 to FIG. 26 are various cross-sectional views of a double-sidedflexible printed circuit board according to another embodiment;

FIG. 27 is a cross-sectional view of a manufacturing process of aflexible circuit board according to FIG. 13;

FIG. 28 to FIG. 31 are cross-sectional views of a manufacturing processof a double-sided flexible printed circuit board according to FIG. 22;

FIG. 32 to FIG. 34 are cross-sectional views of a flexible circuit boardaccording to FIG. 13 mounted on an electronic device;

FIG. 35 is a cross-sectional view of a COF module having a flexiblecircuit board according to embodiments;

FIG. 36 and FIG. 37 are cross-sectional views of a chip package having adouble-sided flexible printed circuit board;

FIG. 38 is a top plan view of a double-sided flexible printed circuitboard according to FIG. 37;

FIG. 39 is a bottom view of a double-sided flexible printed circuitboard according to FIG. 37;

FIG. 40 is a cross-sectional view of a pattern shape of a lead patternpart of an all-in-one chip on film (COF) flexible circuit boardaccording to an embodiment; and

FIG. 41 to FIG. 43 are electronic devices having a flexible circuitboard according to embodiments.

DETAILED DESCRIPTION

Referring to FIG. 1 to FIG. 8, a flexible circuit board may include: asubstrate 100; a wiring pattern layer 200 provided on the substrate 100;a plating layer 300; and a protective layer 400. The substrate 100 maybe a supporting substrate to support the wiring pattern layer 200, theplating layer 300, and the protective layer 400. The substrate 100 mayinclude a bending area BA and a non-bending area NBA except for thebending area. The substrate 100 may include a bending area BA wherebending may occur and a non-bending area NBA other than the bending areaBA.

The substrate 100 may be a flexible substrate. The substrate 100 mayinclude a flexible plastic. For example, the substrate 100 may be apolyimide (PI) substrate. However, the embodiment is not limitedthereto, and may be a substrate made of a polymer material such as,e.g., polyethylene terephthalate (PET) or polyethylene naphthalate(PEN). Accordingly, a flexible circuit board including the substrate 100may be used in various electronic devices having a curved displaydevice. For example, a flexible circuit board including the substrate100 may have flexible characteristics, thereby making it suitable tomount a semiconductor chip on a wearable electronic device. Thesubstrate 100 may be an insulating substrate. The substrate 100 may bean insulating substrate that supports various wiring patterns.

The substrate 100 may have a thickness of 12 μm to 125 μm. For example,the substrate 100 may have a thickness of 50 μm or less. The substrate100 may have a thickness of 20 μm to 40 μm. When the thickness of thesubstrate 100 exceeds 125 μm, a thickness of the entire flexible circuitboard may be increased.

Wiring may be provided on the substrate 100. The wiring may be aplurality of patterned wirings. For example, a plurality of wirings onthe substrate 100 may be provided apart from each other. The wiringpattern layer 200 may be provided on one surface of the substrate 100.The wiring pattern layer 200 may be provided on a bending area BA and anon-bending area NBA on the substrate 100.

An area of the substrate 100 may be larger than an area of the wiringpattern layer 200. A planar area of the substrate 100 may be larger thana planar area of the wiring pattern layer 200. The wiring pattern layer200 may be partially provided on the substrate 100. For example, a lowersurface of the wiring pattern layer 200 may be in contact with thesubstrate 100, and the substrate 100 may be exposed between theplurality of wirings. The wiring pattern layer 200 may include aconductive material. For example, the wiring pattern layer 200 mayinclude a metal material having excellent electrical conductivity. Thewiring pattern layer 200 may include copper (Cu). However, theembodiment is not limited to thereto, and the wiring pattern layer 200may include at least one metal among copper (Cu), aluminum (Al),chromium (Cr), nickel (Ni), silver (Ag), molybdenum (Mo), gold (Au),titanium (Ti), and an alloy thereof.

The wiring pattern layer 200 may be provided to have a thickness of 1 μmto 20 μm. For example, the wiring pattern layer 200 may be provided tohave a thickness of 5 μm to 20 μm. The wiring pattern layer 200 may beprovided to have a thickness of 5 μm to 15 μm. When the thickness of thewiring pattern layer 200 is less than 1 μm, a resistance of the wiringpattern layer 200 may increase. When the thickness of the wiring patternlayer 200 is more than 20 μm, it may be difficult to create a finepattern.

The plating layer 300 may be provided on the wiring pattern layer 200.Two layers of plating layers may be provided on the wiring pattern layer200. The plating layer 300 may include a first plating layer 310 and asecond plating layer 320. The plating layer 300 may be partiallyprovided on the wiring pattern layer 200. The plating layer 300 mayinclude open parts or areas OA1 and OA2 in an area corresponding to thebending area BA. The first plating layer 310 may include a first openarea OA1, and the second plating layer 320 may include a second openarea OA2. A width of the second open area OA2 of the second platinglayer 320 may be larger than a width of the open area OA1 of the firstplating layer 310.

The first plating layer 310 may be partially provided on the wiringpattern layer 200. For example, the first plating layer 310 may beprovided on a non-bending area NBA on the wiring pattern layer 200. Thefirst plating layer 310 may be partially provided on a bending area BAon the wiring pattern layer 200. For example, the first plating layer310 may be provided only on the non-bending area NBA on the wiringpattern layer 200. The first plating layer 310 may not be provided onthe bending area BA on the wiring pattern layer 200. Accordingly, thefirst plating layer 310 may include a first open area OA1 in an areacorresponding to the bending area BA. For example, a width of the firstopen area OA1 may correspond to a width of the bending area BA.

An opened side surface of the first plating layer 310 may be provided ina boundary region between the bending area BA and the non-bending areaNBA. For example, the width of the first open area OA1 may be smallerthan the width of the bending area BA. Both open side surfaces of thefirst plating layer 310 may be provided on the bending area BA. Forexample, the width of the first open area OA1 may be larger than thewidth of the bending area BA. Both open side surfaces of the firstplating layer 310 may be provided on the non-bending area NBA.

The first plating layers 310 may be spaced apart from each other by thefirst open area. For example, a first pattern plating layer 311 adjacentto one end of the bending area may not be connected to a first patternplating layer 312 adjacent to another end of the bending area. The firstpattern plating layer 311 and the first pattern plating layer 312 maypartially overlap the bending area BA. Alternatively, the first patternplating layer 311 and the first pattern plating layer 312 may beprovided only on the non-bending area NBA.

The second plating layer 320 may be provided on the first plating layer310. The second plating layer 320 may be partially provided on the firstplating layer 310. The second plating layer 320 may be provided on anarea of the first plating layer 310 except for an area where theprotective layer 400 is provided on the first plating layer 310. Thesecond plating layer 320 may be provided on an area of the first platinglayer 310 except for an area where the protective layer 400 is providedon the first plating layer 310.

The second plating layer 320 may be provided on an area corresponding toa non-bending area NBA on the first plating layer 310, The secondplating layer 320 may be partially provided on a bending area BA.Alternatively, the second plating layer 320 may be provided only on anarea corresponding to the non-bending area NBA on the first platinglayer 310.

The second plating layer 320 may not be provided on the bending area BA.Accordingly, the second plating layer 320 may include a second open areaOA2. For example, the width of the second open area OA2 may be largerthan the width of the bending area BA. A side surface of the secondplating layer 320 may be spaced apart from a boundary region between thebending area BA and the non-bending area NBA. For example, the width ofthe second open area OA2 may correspond to the width of the bending areaBA. The width of the second open area OA2 may be smaller than the widthof the bending area BA. The second plating layers 320 may be spacedapart from each other by the second open area OA2. For example, a secondpattern plating layer 321 from one end of the bending area BA may not beconnected to a second pattern plating layer 322 from another end of thebending area BA.

The width of the first open area OA1 may be different from that of thesecond open area OA2. The width of the first open area OA1 may besmaller than that of the second open area OA2. The first open area OA1and the second open area OA2 may be located in an area corresponding tothe bending area BA. At least one open area of the first open area OA1and the second open area OA2 may be entirely or partially located on thebending area BA.

The area of the second plating layer 320 may be smaller than that of thefirst plating layer 310. The second plating layer 320 may have a smallerplanar area than a planar area of the first plating layer 310. Onesurface of the wiring pattern layer 200 and a side surface of theplating layer 300 may be exposed in the first open area OA1.

A protective layer 400 may be provided on the first open area OA1 andthe second open area OA2. The protective layer 400 may be in directcontact with one surface of the wiring pattern layer 200 exposed at thefirst open area OA1 and a side surface of the plating layer 300.

A width W1 of the protective layer 400 provided on the first open areaOA1 may be smaller than a width W2 of the protective layer 400 providedon the second open area OA2. The protective layer 400 may be in directcontact with one surface of the wiring pattern layer 200 exposed at thefirst open area OA1, an upper surface of the first plating layer 310,and a side surface of the second plating layer 320 exposed at the secondopen area OA2.

An upper surface of the first plating layer 310 exposed at the secondopen area OA2 may be located at the non-bending area NBA, but theembodiment is not limited thereto. For example, the upper surface of thefirst plating layer 310 exposed at the second open area OA2 may belocated at the bending area BA. Alternatively, the upper surface of thefirst plating layer 310 exposed at the second open area OA2 may belocated in the bending area BA and the non-bending area NBA.

The plating layer 300 may include tin (Sn). For example, the firstplating layer 310 and the second plating layer 320 may include tin (Sn).The wiring pattern layer 200 may be formed of copper (Cu), and the firstplating layer 310 and the second plating layer 320 may be formed of tin(Sn). Although the first plating layer 310 and the second plating layer320 may both be formed of tin (Sn), the first plating layer 310 and thesecond plating layer 320 may be formed in different steps. The firstplating layer 310 may be plated with tin (Sn), and then the protectivelayer 400 may be applied as an insulating pattern, and the secondplating layer 320 may be plated with tin (Sn).

For example, when the manufacturing process of a flexible circuit boardaccording to embodiments includes a heat treatment process such asthermal curing, a diffusion action of copper (Cu) of the wiring patternlayer 200 or tin (Sn) of the plating layer 300 may occur. As thediffusion concentration of copper (Cu) decreases from the first platinglayer 310 to a surface of the second plating layer 320, a content ofcopper (Cu) may be reduced. The content of tin (Sn) may increase fromthe first plating layer 310 to the surface of the second plating layer320.

The first plating layer 310 and the second plating layer 320 may be analloy of tin (Sn) and copper (Cu) due to a chemical action at alamination interface of the wiring pattern layer 200 and the platinglayer 300. The first plating layer 310 and the second plating layer 320may have different contents of tin (Sn) and copper (Cu). The firstplating layer 310 directly contacting the copper wiring pattern layermay have a copper (Cu) content more than a copper (Cu) content of thesecond plating layer 320. Alternatively, the first plating layer 310 mayinclude an alloy of tin (Sn) and copper (Cu), and the second platinglayer 320 may include tin (Sn). The plating layer according to theembodiment may prevent electrochemical migration resistance due to adiffusion phenomenon of Cu/Sn, and may prevent short-circuit defects dueto metal growth. However, the embodiment is not limited thereto, and mayinclude any one of a Ni/Au alloy, gold (Au), electroless nickelimmersion gold (ENIG), a Ni/Pd alloy, and organic solderabilitypreservative (OSP).

The first plating layer 310 may have a thickness different from that ofthe second plating layer 320. A thickness T1 of the first plating layer310 may be smaller than a thickness T2 of the second plating layer 320.For example, the first plating layer 310 may have a thickness of 0.1 μmor less. For example, the second plating layer 320 may have a thicknessof 1 μm or less. The total thickness of the plating layer 300 may be 1.1μm or less. Thicknesses of the first plating layer 310 and the secondplating layer 320 may be 1.1 μm or less.

The protective layer 400 may cover an upper surface of the wiringpattern layer 200 on the bending area BA and a part of the first platinglayer 310 and may be provided to be wider than the bending area BA. Theprotective layer 400 may be in contact with the wiring pattern layer200, the first plating layer 310, and the second plating layer 320. Theprotective layer 400 may be in contact with the upper surface of thewiring pattern layer 200 on the bending area, a part of an upper surfaceof the first plating layer 310, and the second plating layer 320. Theprotective layer 400 may be in direct contact with an upper surface ofthe wiring pattern layer 200 of the bending area BA to the first openarea OA1, an upper surface and a side surface of the first plating layer310 outside the bending area BA to the first open area OA1, and a sidesurface of the second plating layer 320.

As the protective layer 400 according to the embodiment may directlycontact the wiring pattern layer 200, the first plating layer 310, andthe second plating layer 320 simultaneously, removal of a protectivelayer 400 may be prevented, thereby improving reliability of theflexible circuit board. The protective layer 400 may cover one sidesurface and the upper surface of the first plating layer 310. Theprotective layer 400 may be overlapped upward and downward with thefirst plating layer 310. For example, the protective layer 400 mayoverlap the first plating layer 310 in the non-bending area NBA and/orthe bending area BA.

A first overlapping region CA1 may be a region in which the firstplating layer 310 and the protective layer 400 may be in contact witheach other, and a second overlapping region CA2 may be a region in whichthe first plating layer 310 and the plating layer 400 may be in contactwith each other. The first overlapping region CA1 and the secondoverlapping region CA2 may be a peripheral region of an open areaadjacent to the first open area OA1. The first overlapping region CA1and the second overlapping region CA2 may be located on a bending areaand/or a non-bending area.

A width of the first overlapping region CA1 or the second overlappingregion CA2 may be 400 μm or more. The width of the first overlappingregion CA1 or the second overlapping region CA2 may be smaller than thewidth of the bending area BA. For example, the widths of the firstoverlapping region CAI and the second overlapping region CA2 may besmaller than that of the bending area BA.

The widths of the first overlapping region CA1 and the secondoverlapping region CA2 may be corresponding to or different from eachother. Referring to FIG. 3, the width of the first overlapping regionCA1 may be equal to the width of the second overlapping region CA2.Referring to FIG. 4, the width of the first overlapping region CA1 maybe different from that of the second overlapping region CA2. The widthof the first overlapping region CA1 may be smaller than the width of thesecond overlapping region CA2.

A side surface 400S of the protective layer 400 may have variouscross-sectional shapes. A side surface 400S of the protective layer 400may include an inclined surface or a vertical surface. For example,referring to FIG. 1, the side surface 400S of the protective layer 400may include an inclined surface. A contact area of the protective layer400 with the second plating layer 320 may be increased, therebypreventing removal of the protective layer 400.

The side surface 4008 of the protective layer 400 may include a curvedinclined surface. For example, as the inclination angle with respect tothe first plating layer 310 becomes closer to the first plating layer310, the side surface 400S of the protective layer 400 may increase. Theside surface 400S of the protective layer 400 may have an acute anglewith respect to the first plating layer 310.

Referring to FIG. 2, the side surface 400S of the protective layer 400may include an inclined surface. The side surface 400S of the protectivelayer 400 may include a straight inclined surface. For example, theinclination angle of the side surface 400S of the protective layer 400and the first plating layer 310 may be constant regardless of distancefrom the first plating layer 310. The side surface 4005 of theprotective layer 400 may be at an acute angle with respect to the firstplating layer 310.

Referring to FIGS. 3 and 4, the side surface 400S of the protectivelayer 400 may include a vertical surface. The side surface 400S of theprotective layer 400 may include a straight inclined surface. Forexample, the side surface 400S of the protective layer 400 may be at aninclination angle of 90 degrees with the first plating layer 310 or thelike.

The protective layer 400 may include an insulating material. Theprotective layer 400 may be a resist layer. For example, the protectivelayer 400 may be a solder resist layer containing an organic polymermaterial. For example, the protective layer 400 may include an epoxyacrylate resin. The protective layer 400 may include a resin, a curingagent, a photo initiator, a pigment, a solvent, a filler, an additive,and an acrylic monomer. However, the embodiment is not limited thereto,and the protective layer 400 may be any one of a photo-solder resistlayer, a cover-lay, or a polymer material.

The protective layer 400 may be provided to have a larger thickness thanthe plating layer 300. A thickness T3 of the protective layer 400 may belarger than the thickness T2 of the second plating layer 320.Accordingly, an upper surface of the protective layer 400 may beprovided higher than an upper surface of the second plating layer 320.Since the upper surface of the protective layer 400 is provided higherthan the upper surface of the second plating layer 320, the protectivelayer 400 may have a step with the second plating layer 320.

The thickness of the protective layer 400 at the bending area may bedifferent from that of the non-bending area. The thickness of theprotective layer 400 on the bending area may be larger than that of thefirst protective layer 410 on the first overlapping region CA1. Thethickness of the protective layer 400 on the bending area may be largerthan that of the first protective layer 410 on the second overlappingregion CA2.

A thickness T3 of the protective layer 400 in the bending area may be 1μm to 20 μm. For example, the thickness T3 of the protective layer 400in the bending area may be 5 μm to 20 μm. The protective layer 400 maybe integrally formed. Accordingly, removal of the protective layer 400according to the embodiment may be prevented, and reliability of theflexible circuit board may be improved. When the flexible circuit boardaccording to embodiments is bent, stress due to tension may be dispersedentirely in the protective layer 400 integrally formed, and reliabilitymay be improved. Efficiency of the process of forming the flexiblecircuit board according to the embodiments may be improved.

Referring to FIG. 5 to FIG. 8, a double-sided flexible circuit board mayinclude a substrate 100 having a bending area and a non-bending area, afirst wiring pattern layer 210 provided on a bending area and anon-bending area on one surface of the substrate, a first plating layer310 provided on the first wiring pattern layer 210 and including an openarea in an area corresponding to the bending area, a second platinglayer 320 provided on the first plating layer 310, a first protectivelayer 410 directly contacting one surface of the first wiring patternlayer 210 exposed at the open area, a side surface of the first platinglayer 210, and a side surface of the second plating layer 320, a secondwiring pattern layer 220 provided on a bending area and a non-bendingarea on another surface opposite to the one surface of the substrate, athird plating layer 330 provided on the second wiring pattern layer 220,a fourth plating layer 340 provided on the third plating layer 330, anda second protective layer 420 provided on an area corresponding to thebending area on the other surface of the substrate. The first protectivelayer 410 may be provided higher than an upper surface of the secondplating layer 320.

The wiring pattern layer 200 may be provided on both sides of thesubstrate 100. The wiring pattern layer 200 may include a first wiringpattern layer 210 and a second wiring pattern layer 220. The firstwiring pattern layer 210 may be provided on one surface of the flexiblesubstrate 100 and the second wiring pattern layer 220 may be provided onthe other surface opposite to the one surface of the flexible substrate100.

A thickness of the first wiring pattern layer 210 may correspond to athickness of the second wiring pattern layer 220. The thickness of thefirst wiring pattern layer 210 and the second wiring pattern layer 220may be 1 μm to 20 μm, respectively. The first plating layer 310 may beprovided on the first wiring pattern layer 210. The third plating layer330 may be provided on the second wiring pattern layer 220.

At least one of the first plating layer 310 and the third plating layer330 may include a first open area OA1. For example, referring to FIG. 5,one of the first plating layer 310 and the third plating layer 330 mayinclude the first open area OA1. The first plating layer 310 may includethe first open area OA1. For example, referring to FIG. 7 and FIG. 8,the first plating layer 310 and the third plating layer 330 may includethe first open area OA1, respectively.

Referring to FIG. 7 and FIG. 8, the third plating layer 330 may beprovided on the non-bending area. The second protective layer 420 maycover a part of upper surfaces of the second wiring pattern layer 220and the third plating layer 330 on the bending area, and may be providedwider than the bending area. The fourth plating layer 340 may beprovided on an area except for the area where the second protectivelayer 420 is provided. The second protective layer 420 may be providedhigher than an upper surface of the fourth plating layer 340.

The second plating layer 320 may be provided on the first plating layer310. The fourth plating layer 340 may be provided on the third platinglayer 330. At least one of the second plating layer 320 and the fourthplating layer 340 may include a second open area OA2. For example,referring to FIG. 5, one of the second plating layer 320 and the fourthplating layer 340 may include the second open area OA2. The secondplating layer 320 may include the second open area OA2. A width W1 ofthe first open area OA1 may be different from a width W2 of the secondopen area OA2. The width W1 of the first open area OA1 may be smallerthan the width W2 of the second open area OA2.

Referring to FIGS. 7 and 8, the second plating layer 320 and the fourthplating layer 340 may include the second open area OA2, respectively.Referring to FIG. 6, a location of the first protective layer 410 may bedifferent from a location of the second protective layer 420. Forexample, the first plating layer 310 may be provided on the first wiringpattern layer 210 on one surface of the substrate 100, and the firstprotective layer 410 may be provided on the first plating layer 310. Thesecond wiring pattern layer 220 may be provided on the other surface ofthe substrate 100, and the third plating layer 330, the fourth platinglayer 340, and the second protective layer 420 may be sequentiallyprovided on the second wiring pattern layer 220.

Two or more protective layers may be provided on at least one of onesurface and the other surface of the substrate 100. For example, thefirst protective layer 410 may be provided on one surface of thesubstrate 100, and the second protective layer 420 may be provided onthe other surface of the substrate 100. Two or more protective layershaving different shapes may be provided on at least one of one surfaceand the other surface of the substrate 100. For example, the firstprotective layer 410 may have a different shape from the secondprotective layer 420. A cross-sectional shape of at least one of thefirst protective layer 410 and the second protective layer 420 may beT-shaped.

The first protective layer 410 may be provided on at least a part of thebending area BA. The first protective layer 410 may be provided entirelyon the bending area BA. The first protective layer 410 may be providedon the entire bending area BA and a part of the non-bending area NBA.The first protective layer 410 may be provided on the second platinglayer 320. In addition, the second protective layer 420 may be providedon the fourth plating layer 340.

At least one of the first protective layer 410 and the second protectivelayer 420 may have different widths for its top surface and bottomsurface. For example, referring to FIG. 5, one of the first protectivelayer 410 and the second protective layer 420 may have an upper surfaceand a lower surface having different widths. A width W2 of the uppersurface and a width W1 of the lower surface of the first protectivelayer 410 may be different. The width W2 of the upper surface of thefirst protective layer 410 may be larger than the width W1 of the lowersurface thereof.

For example, referring to FIGS. 7 and 8, the first protective layer 410and the second protective layer 420 may have different widths on theupper surface and the lower surface, respectively. Referring to FIG. 7,the width W2 of the upper surface and the width W1 of the lower surfaceof the first protective layer 410 may be different. The width W2 of theupper surface of the first protective layer 410 may be larger than thewidth W1 of the lower surface thereof. A width W2 of the upper surfaceand a width W3 of the lower surface of the second protective layer 420may be different. The width W2 of the upper surface of the secondprotective layer 420 may be larger than the width W3 of the lowersurface thereof. The width W1 of the lower surface of the firstprotective layer 410 may be different from the width W3 of the lowersurface of the second protective layer 420.

Referring to FIG. 8, the width W2 of the upper surface and the width W1of the lower surface of the first protective layer 410 may be different.The width W2 of the upper surface of the first protective layer 410 maybe larger than the width WI of the lower surface thereof. The width W2of the upper surface and the width W1 of the lower surface of the secondprotective layer 420 may be different. The width W2 of the upper surfaceof the second protective layer 420 may be larger than the width W1 ofthe lower surface thereof. The width W1 of the lower surface of thefirst protective layer 410 may correspond to the width W1 of the lowersurface of the second protective layer 420.

At least one of the first protective layer 410 and the second protectivelayer 420 may be in contact with the wiring pattern layer 200. Forexample, referring to FIG. 5, one protective layer of the firstprotective layer 410 and the second protective layer 420 may be incontact with the wiring pattern layer 200. The first protective layer410 may be in contact with the wiring pattern layer 200. The firstprotective layer 410 may receive a tensile force, and the secondprotective layer 420 may be bent in a direction to receive a compressiveforce. As one surface of the first protective layer 410 contacts thewiring pattern layer 200, it may be possible to prevent a crack frombeing generated in the first wiring pattern layer 210 and the platinglayer 300 at a portion when the flexible circuit board is folded.Therefore, reliability of the flexible circuit board may be improved.

For example, referring to FIGS. 7 and 8, the first protective layer 410may be in contact with the first wiring pattern layer 210, and thesecond protective layer 420 may be in contact with the second wiringpattern layer 220, respectively. The first protective layer 410 or thesecond protective layer 420 may be bent in a direction to receive atensile force. Accordingly, as one surface of the first protective layer410 or one surface of the second protective layer 420 contacts thewiring pattern layer, it may be possible to prevent a crack from beinggenerated in the first or second wiring pattern layer 210, 220 and/orthe plating layers 310, 320, 330, and 340 at a portion thereof when theflexible circuit board is folded. Therefore, reliability of the flexiblecircuit board may be improved.

A thickness of the first protective layer 410 may correspond to ordifferent from a thickness of the second protective layer 420. Thethickness of the protective layer may refer to a measurement at thebending area. For example, referring to FIG. 5, the thickness T3 of thefirst protective layer 410 may be different from the thickness T4 of thesecond protective layer 420. The thickness T3 of the first protectivelayer 410 may be larger than the thickness T4 of the second protectivelayer 420. The thickness of the first protective layer 410 may be 10 μmto 20 μm, and the thickness of the second protective layer 420 may be 5μm to 15 μm.

The first protective layer 410 may receive a tensile force, and thesecond protective layer 420 may be bent in a direction to receive acompressive force. Since the first protective layer 410 receiving atensile force has a larger thickness than the second protective layer420 receiving a compressive force, the first wiring pattern layer 210and/or the plating layers 310 and 320 may be prevented from beingcracked at a portion that receives tension when folding the flexiblecircuit board. Therefore, reliability of the flexible circuit board maybe improved.

For example, referring to FIGS. 7 and 8, the thickness T3 of the firstprotective layer 410 may correspond to the thickness T3 of the secondprotective layer 420. The thickness of the first protective layer 410may be 1 μm to 20 μm, and the thickness of the second protective layer420 may be 1 μm to 20 μm.

The first protective layer 410 and the second protective layer 420 maybe in contact with the first and second wiring pattern layers 210 and220, respectively, the thickness of the first protective layer 410 maybe 10 μm to 20 μm, and the thickness of the second protective layer 420may be 5 μm to 15 μm. The first protective layer 410 may receive atensile force, and the second protective layer 420 may be bent in adirection to receive a compressive force. Since the first protectivelayer 410 receiving a tensile force has a larger thickness than thesecond protective layer 420 receiving a compressive force, the firstwiring pattern layer 210 and/or the plating layers 310 and 320 may beprevented from being cracked at a portion that has or receives tensionwhen folding the flexible circuit board. Therefore, reliability of theflexible circuit board may be improved.

Referring to FIG. 5, FIG. 7 and FIG. 8, an outer side of one end of thebending area may include a first overlapping region in which the firstplating layer and the first protective layer may be in contact with eachother, and an outer side of another end of the bending area may includea second overlapping region in which the first plating layer and thefirst protective layer may be in contact with each other. A width of thefirst overlapping region may correspond to or may be different from awidth of the second overlapping region. The outer side of one end of thebending area may include a third overlapping region in which the thirdplating layer and the second protective layer are in contact with eachother, and the outer side of the other end of the bending area mayinclude a fourth overlapping region in which the third plating layer andthe second protective layer may be in contact with each other.

Referring to FIG. 7, the width of the first overlapping region CAI maycorrespond to the width of the second overlapping region CA2. The widthof the third overlapping region CA3 may correspond to the width of thefourth overlapping region CA4. The width of the first overlapping regionCA1 may be smaller than the width of the third overlapping region CA3.The width of the second overlapping region CA2 may be smaller than thewidth of the fourth overlapping region CA4.

Referring to FIG. 8, the width of a contact region of the firstprotective layer 410 and the first wiring pattern layer 210 may be equalto the width of a contact region of the second protective layer 420 andthe second wiring pattern layer 220. The width of the first overlappingregion CA1 may correspond to the width of the second overlapping regionCA2. The width of the first overlapping region CA1 may correspond to thewidth of the third overlapping region CA3. The width of the secondoverlapping region CA2 may correspond to the width of the fourthoverlapping region CA4.

Referring to FIG. 8, the width W1 of the contact region of the firstprotective layer 410 and the first wiring pattern layer 210 may be equalto the width WI of the contact region of the second protective layer 420and the second wiring pattern layer 220. At this point, the thickness ofthe first protective layer 410 and the thickness of the secondprotective layer 420 may be same. The first protective layer 410 and thesecond protective layer 420 may have corresponding shapes andthicknesses. Stress due to deformation on one surface and the othersurface of the substrate may be minimized. By increasing the contactarea of the first and second protective layers 410/420 and the wiringpattern layer 200 and the plating layer 300, removal of the protectivelayers 410/420 may be prevented. The first and second protective layers410/420 have corresponding shapes, and thus process efficiency may beimproved.

In a double-sided flexible printed circuit board according to theembodiments, a protective layer on a side receiving a tensile force maycontact a wiring pattern layer and thus cracking and breakage of thewiring pattern layer and/or a plating layer due to bending may beprevented, and reliability may be improved as a result.

The double-sided flexible printed circuit board may include a firstprotective layer 410 provided between the first plating layer 310 andthe second plating layer 320. The double-sided flexible printed circuitboard may include a structure of the first protective layer 410 in whicha portion is buried between the first plating layer 310 and the secondplating layer 320, and thus a tensile force of a bending area may bebuffered, and cracking of a wiring pattern layer and a plating layer maybe prevented.

In the double-sided flexible printed circuit board, as at least oneprotective layer of the first protective layer 410 and second protectivelayer 420 may be in contact with the wiring pattern layer 200, a crackdue to a change in tensile force during bending may be prevented.Accordingly, a semiconductor chip may be mounted in a narrow region ofan electronic device in high density, and a high-resolution display maybe implemented. Appearance defects and reliability degradation due togeneration of Sn particles may be prevented.

Hereinafter, a method of manufacturing a double-sided flexible printedcircuit board according to the embodiments is described with referenceto FIG. 9 to FIG. 12. The manufacturing method of a flexible circuitboard may include preparing a substrate having a thickness of 12 μm to125 μm, forming a wiring pattern layer having a thickness of 1 μm to 20μm on one surface of the substrate, forming a first plating layer havinga thickness of 0.1 μm or less on an area except for a bending area onthe first wiring pattern layer, providing a protective layer having athickness of 1 μm to 20 μm so as to cover the first wiring pattern layerand a part of the first plating layer on the bending area, and providinga second plating layer having a thickness of 1 μm or less in an areaexcept for the area where the protective layer is provided on the firstplating layer. Forming the first plating layer in an area except for thebending area on the wiring pattern layer may include providing a maskinglayer at the bending area on the wiring pattern layer, plating the firstplating layer on the non-bending area, and removing the masking layer.

Referring to FIG. 9, a double-sided flexible printed circuit board maybe manufactured according to a dry film masking method or a photo solderresist (PSR) printing method. First, a first wiring pattern layer 210and a second wiring pattern layer 220 may be prepared on both sides of asubstrate 100. A circuit may be formed on both surfaces of a substrate100. The substrate 100 may be a polyimide flexible substrate, and awiring pattern may include copper.

An upper sacrificial layer T1 may be formed by laminating a dry film onthe first wiring pattern layer 210 or by printing a photo solder resistlayer. A lower sacrificial layer B1 may be formed by laminating a dryfilm on the second wiring pattern layer 220 or by printing a photosolder resist layer. Next, a mask may be provided on the uppersacrificial layer T1 and the lower sacrificial layer B1, and an exposurestep for exposing ultraviolet rays may be performed.

A development step of removing the unexposed upper sacrificial layer T1and the lower sacrificial layer B1 may be performed. Accordingly, apatterned upper sacrificial layer P1 and a patterned lower sacrificiallayer P2 may be formed. Next, a first plating layer 310 may be formed ina peripheral region of the patterned upper sacrificial layer P1. A thirdplating layer 330 may be formed in the peripheral region of thepatterned lower sacrificial layer P2.

The patterned upper sacrificial layer P1 and the patterned lowersacrificial layer P2 may then be peeled off. A first plating layer 310and a third plating layer 330 having a first open area may be formed.Each of the first plating layer 310 and the third plating layer 330 maybe tin-plated.

Next, first and second protective layers 410 and 420 covering sidesurfaces and parts of upper surfaces of the first plating layer 310 andthe third plating layer 330 may be provided while filling a first openarea. Upper surfaces of the first and second protective layers 410 and420 may have a larger width than that of the bending area.

Next, second and fourth plating layers 320 and 340 may be formed in theperipheral region of the first and second protective layers 410 and 420.The second and fourth plating layers 320 and 340 may be formed in anarea where the first and second protective layers 410 and 420 are notprovided with a thickness smaller than that of the first and secondprotective layers 410 and 420. Accordingly, side surfaces of the firstand second protective layers 410 and 420 may contact the second andfourth plating layers 320 and 340. Each of the second plating layer 320and the fourth plating layer 340 may be tin-plated.

Referring to FIG. 10, a double-sided flexible printed circuit board maybe manufactured according to a PET masking method. First, a first wiringpattern layer 210 and a second wiring pattern layer 220 may be preparedon both sides of a flexible substrate 100. A circuit may be formed onboth surfaces of a flexible substrate 100. The flexible substrate 100may be a polyimide flexible substrate, and a wiring pattern may includecopper.

Next, a PET masking film may be punched to prepare a PET masking filmhaving a through-hole. A patterned upper sacrificial layer P1 may thenbe formed by laminating a PET masking film having through holes on thefirst wiring pattern layer 210. A patterned lower sacrificial layer P2may be formed by laminating a PET masking film having through holes onthe second wiring pattern layer 220.

Next, a first plating layer 310 may be formed in a through hole of thepatterned upper sacrificial layer P1. A third plating layer 330 may beformed in a through hole of the patterned lower sacrificial layer P2.The patterned upper sacrificial layer P1 and the patterned lowersacrificial layer P2 may then be peeled off. Accordingly, a firstplating layer 310 and a third plating layer 330 having a first open areamay be formed. Each of the first plating layer 310 and the third platinglayer 330 may be tin-plated.

Next, protective layers 410 and 420 covering side surfaces and parts ofupper surfaces of the first plating layer 310 and the third platinglayer 330 may be provided while filling the first open area. Uppersurfaces of the protective layers 410 and 420 may have a larger widththan that of the bending area.

Second and fourth plating layers 320 and 340 may then be formed in theperipheral area of the first and second protective layers 410 and 420.The second and fourth plating layers 320 and 340 may be formed in anarea where the protective layers 410 and 420 are not provided with athickness smaller than that of the protective layer. Side surfaces ofthe first and second protective layers 410 and 420 may contact thesecond and fourth plating layers 320 and 340. The second plating layer320 and the fourth plating layer 340 may be tin-plated respectively.

Referring to FIG. 11, a double-sided flexible printed circuit board maybe manufactured according to a photoresist (PR) printing or gravureprinting method. First, a first wiring pattern layer 210 and a secondwiring pattern layer 220 may be prepared on both sides of a flexiblesubstrate 100. A circuit may be formed on both surfaces of a flexiblesubstrate 100. The flexible substrate 100 may be a polyimide flexiblesubstrate, and a wiring pattern may include copper.

Next, a photoresist ink may be applied on the first wiring pattern layer210 to form a patterned upper sacrificial layer P1. A photoresist inkmay be printed on the second wiring pattern layer 220 to form apatterned lower sacrificial layer P2. A first plating layer 310 may beformed in the peripheral region of the patterned upper sacrificial layerP1. A third plating layer 330 may be formed in the peripheral region ofthe patterned lower sacrificial layer P2. The patterned uppersacrificial layer P1 and the patterned lower sacrificial layer P2 maythen be peeled off. A first plating layer 310 and a third plating layer330 having a first open area may be formed. The first plating layer 310and the third plating layer 330 may be tin-plated respectively.

Next, first and second protective layers 410 and 420 covering sidesurfaces and parts of upper surfaces of the first plating layer 310 andthe third plating layer 330 may be provided while filling the first openarea. Upper surfaces of the protective layers may have a larger widththan that of the bending area. Second and fourth plating layers 320 and340 may then be formed in the peripheral region of the first and secondprotective layers 410 and 420. The second and fourth plating layers 320and 340 may be formed in an area where the first and second protectivelayers 410 and 420 are not provided with a thickness smaller than thatof the protective layer. Side surfaces of the protective layers maycontact the second and fourth plating layers 320 and 340. The secondplating layer 320 and the fourth plating layer 340 may be tin-platedrespectively.

Referring to FIG. 12, a double-sided flexible printed circuit board maybe manufactured according to a Spurt Jar plating method. First, a firstwiring pattern layer 210 and a second wiring pattern layer 220 may beprepared on both sides of a flexible substrate 100. A circuit may beformed on both surfaces of a flexible substrate 100. The flexiblesubstrate 100 may be a polyimide flexible substrate, and a wiringpattern may include copper.

Next, a first plating layer 310 and a third plating layer 330 having afirst open area may be formed in an area corresponding to a bending areaby performing Spurt Jar plating. The first plating layer 310 and thethird plating layer 330 may be tin-plated respectively. Protectivelayers covering side surfaces and parts of upper surfaces of the firstplating layer 310 and the third plating layer 330 may be provided whilefilling the first open area. Upper surfaces of the protective layers mayhave a larger width than that of the bending area.

Second and fourth plating layers 320 and 340 may then be formed in theperipheral region of the first and second protective layers 410 and 420.The second and fourth plating layers 320 and 340 may be formed in anarea where the first and second protective layers 410 and 420 are notprovided with a thickness smaller than that of the protective layer.Side surfaces of the protective layers may contact the second and fourthplating layers 320 and 340. The second plating layer 320 and the fourthplating layer 340 may be tin-plated respectively.

Referring to FIG. 13 to FIG. 20, a flexible circuit board according toanother embodiment may include a substrate 100, a wiring pattern layer200 provided on the substrate 100, a plating layer 300, and a protectivelayer 400. Same drawing symbols or labels may be assigned to the samecompositions as those of the previous embodiment described above, andredundant description has been omitted.

The flexible circuit board may include a substrate 100 having a bendingarea BA and a non-bending area NBA, a wiring pattern layer 200 providedon a bending area and a non-bending area on the substrate 100, a platinglayer 300 provided on the wiring pattern layer and including open areasOA1 and OA2 in an area corresponding to the bending area, and aprotective layer 400 directly contacting one surface of the wiringpattern layer 200 exposed at the open areas OA1 and OA2 and a sidesurface of the plating layer 300. The protective layer 400 may beprovided to have a larger thickness than a thickness of the platinglayer 300.

An upper protective layer 412 and a lower protective layer 411 may beprovided in two layers on a same surface of the substrate 100. The upperprotective layer 412 may have a larger width than a width of the lowerprotective layer 411. On the same surface of the substrate 100, twoprotective layers having different shapes may be provided.

Referring to FIG. 13, FIG. 15, and FIG. 16, the width of the second openarea OA2 of the second plating layer 320 may correspond to the width ofthe first open area OA1 of the first plating layer 310. The area of thesecond plating layer 320 may be the same as the area of the firstplating layer 310. A planar area of the second plating layer 320 maycorrespond to a planar area of the first plating layer 310.

A lower protective layer 411 may be provided on one surface of a wiringpattern layer 200 exposed by the first open area OA1 and the second openarea OA2. A width W1 of the lower protective layer 411 provided on thefirst open area OA1 may correspond to a width W1 of the lower protectivelayer 411 provided on the second open area OA2.

Alternatively, referring to FIG. 14, the width of the first open areaOA1 may be similar to the width of the second open area OA2. The widthof the first open area OA1 may be larger than the width of the secondopen area OA2 due to the inclined surface of the lower protective layer411. The area of the second plating layer 320 may be larger than that ofthe first plating layer 310. The second plating layer 320 may have alarger planar area than that of the first plating layer 310.

A lower protective layer 411 may be provided on one surface of a wiringpattern layer 200 exposed by the first open area OM and the second openarea OA2. A width W1 of the lower protective layer 411 provided on thefirst open area OA1 may be larger than a width W1 of the lowerprotective layer 411 provided on the second open area OA2 due to aninclined surface 411 s of the lower protective layer 411.

For example, referring to FIG. 17 to FIG. 20, the second plating layer320 may be partially provided on the first plating layer 310. The secondplating layer 320 may be provided on an area of the first plating layer310 except for an area where the lower protective layer 411 is providedon the first plating layer 310. The second plating layer 320 may beprovided on an area of the first plating layer 310 except for the areawhere the lower protective layer 411 is provided on the first platinglayer 310.

The second plating layer 320 may be partially provided on the firstplating layer 310. For example, the second plating layer 320 may beprovided on an area corresponding to the non-bending area NBA except forthe bending area on the first plating layer 310. The second platinglayer 320 may not be provided on the bending area BA. For example, thesecond plating layer 320 may be provided on an area corresponding to thenon-bending area NBA on the first plating layer 310 and on an areacorresponding to at least a part of the bending area BA. The secondplating layer 320 may be partially provided on the non-bending area NBAand the bending area BA.

The second plating layer 320 may include a second open area OA2. Forexample, the width of the second open area OA2 may be larger than thatof the bending area BA. A side surface of the second plating layer 320may be spaced apart at a boundary region between the bending area BA andthe non-bending area NBA. For example, the width of the second open areaOA2 may correspond to the width of the bending area BA. For example, thewidth of the second open area OA2 may be smaller than the width of thebending area BA. The second plating layer 320 may be spaced apart fromeach other by the second open area OA2. For example, a second patternplating layer 321 may not be connected to a second pattern plating layer322.

The width of the first open area OA1 may be different from the width ofthe second open area OA2. The width of the first open area OA1 may besmaller than the width of the second open area OA2. The area of thesecond plating layer 320 may be smaller than that of the first platinglayer 310. The second plating layer 320 may have a smaller planar areathan a planar area of the first plating layer 310.

A lower protective layer 411 may be provided on the first open area OA1and the second open area OA2. A width W1 a of the lower protective layer411 provided on the first open area OA1 may be smaller than a width W1 bof the lower protective layer 411 provided on the second open area OA2.

The plating layer 300 may have a two-layer structure. The first platinglayer 310 and the second plating layer 320 may be sequentially providedon the wiring pattern layer 200. The first plating layer 310 and thesecond plating layer 320 may be formed as two layers on the wiringpattern layer 200 in order to prevent formation of whiskers.Accordingly, a short circuit among the patterns of the wiring patternlayer 200 may be prevented.

The plating layer 300 may include tin (Sn). For example, the firstplating layer 310 and the second plating layer 320 may include tin (Sn).The wiring pattern layer 200 may be formed of copper (Cu), and the firstplating layer 310 and the second plating layer 320 may be formed of tin(Sn). When the plating layer 300 includes tin (Sn), oxidation of thewiring pattern layer 200 may be prevented due to excellent corrosionresistance of tin (Sn). The first plating layer 310 and the secondplating layer 320 are formed of the same tin (Sn), but may be formed ina separate process. An electrical conductivity of the plating layer 300may be lower than electrical conductivity of the wiring pattern layer200. The plating layer 300 may be electrically connected to the wiringpattern layer 200.

Referring to FIG. 13 to FIG. 16, a process may be performed such that alower protective layer 411, such as an insulating pattern, may becoated, the first plating layer 310 may be plated with tin (Sn), thenthe second plating layer 320 may be plated with tin (Sn), and an upperprotective layer 412, such as an insulating pattern, may be provided.Referring to FIG. 17 to FIG. 20, a process may be performed such thatthe first plating layer 310 may be plated with tin (Sn), then a lowerprotective layer 411, such as an insulating pattern, may be coated, thesecond plating layer 320 may be plated with tin (Sn), and a upperprotective layer 412, such as an insulating pattern, may be provided.

For example, when the manufacturing process of a flexible circuit boardaccording to the embodiments includes a heat treatment process such asthermal curing, a diffusion action of copper (Cu) of the wiring patternlayer 200 or tin (Sn) of the plating layer 300 may occur. As a diffusionconcentration of copper (Cu) decreases from the first plating layer 310to a surface of the second plating layer 320, a content of copper (Cu)may be reduced. A content of tin (Sn) may increase from the firstplating layer 310 to the surface of the second plating layer 320.

The protective layer 400 may include a lower protective layer 411 and anupper protective layer 412. The lower protective layer 411 may beprovided on an area corresponding to a bending area BA of the wiringpattern layer 200, and the upper protective layer 412 may besequentially provided on the lower protective layer 411.

Referring to FIG. 13 to FIG. 16, the lower protective layer 411 maycover an upper surface of the wiring pattern layer 200 on an areacorresponding to the bending area BA, and may be provided to have awidth corresponding to the bending area BA. However, the embodiment isnot limited thereto, and the width of the lower protective layer 411 maybe smaller than the width of the bending area BA or larger than thewidth of the bending area BA.

The lower protective layer 411 may be in contact with the wiring patternlayer 200, the first plating layer 310, and the second plating layer320. The lower protective layer 411 may contact an upper surface of thewiring pattern layer 210 on an area corresponding to the bending areaBA, a side surface of the first plating layer 310, and a side surface ofthe second plating layer 320. The lower protective layer 411 maydirectly contact an upper surface of the wiring pattern layer 210exposed at an open area, the side surface of the first plating layer310, and the side surface of the second plating layer 320. As the lowerprotective layer 411 may directly contact the wiring pattern layer 200,the first plating layer 310, and the second plating layer 320simultaneously, removal of the lower protective layer 411 may beprevented, thereby improving reliability of the flexible circuit board.

Alternatively, referring to FIG. 17 to FIG. 20, a part of the lowerprotective layer 411 may cover an upper surface of the first platinglayer 310. For example, a part of the lower protective layer 411 maycover an upper portion of the first plating layer 310 extending from thebending area BA to the non-bending area NBA. However, the embodiment isnot limited thereto, and an open upper surface of the lower protectivelayer 411 may be located in the bending area BA and/or the non-bendingarea NBA.

One surface and another surface opposite to the one surface of the lowerprotective layer 411 may be provided on the bending area BA.Alternatively, one surface and the other surface opposite to the onesurface of the lower protective layer 411 may be provided on a boundaryregion between the bending area BA and the non-bending area NBA.Alternatively, one surface and the other surface opposite to the onesurface of the lower protective layer 411 may be provided on thenon-bending area NBA. Accordingly, stresses that may occur duringbending may be dispersed at two different interfaces. Due to the lowerprotective layer 411, stresses that may occur during bending may bedispersed at an interface between the lower protective layer 411 and thefirst plating layer 310, and at an interface between the lowerprotective layer 411 and the second plating layer 320. Accordingly, itmay be possible to prevent damage due to cracking of the flexiblecircuit board, and thus reliability may be improved.

The lower protective layer 411 may cover an upper surface of the wiringpattern layer 200 on the bending area BA and a part of the first platinglayer 310, and may be provided to have a larger width than the width ofthe first open area OA1. The lower protective layer 411 may be incontact with the wiring pattern layer 200, the first plating layer 310,and the second plating layer 320. The lower protective layer 411 may bein contact with an upper surface of the wiring pattern layer 200 on thebending area BA, a part of an upper surface of the first plating layer310, and the second plating layer 320.

The lower protective layer 411 may be in direct contact with an uppersurface of the wiring pattern layer 200 exposed at an open area, anupper surface and a side surface of the first plating layer 310, and aside surface of the second plating layer 320. As the lower protectivelayer 411 may be in direct contact with the wiring pattern layer 200,the first plating layer 310, and the second plating layer 320simultaneously, removal of the lower protective layer 411 may beprevented, thereby improving reliability of the flexible circuit board.

The lower protective layer 411 may cover one side surface and the uppersurface of the first plating layer 310. Accordingly, a contact areabetween the lower protective layer 411 and the first plating layer 310may be increased. An adhesive strength of the lower protective layer 411to the first plating layer 310 may be increased, thereby improvingreliability.

The lower protective layer 411 may overlap the first plating layer 310.The lower protective layer 411 may overlap the first plating layer 310on the bending area BA and/or the non-bending area NBA. A firstoverlapping region CA1 may be a region in which the first patternplating layer 311 and the lower protective layer 411 may be in contactwith each other, and a second overlapping region CA2 may be a region inwhich the first pattern plating layer 312 and the lower protective layer411 may be in contact with each other.

A width of the first overlapping region CA1 or the second overlappingregion CA2 may be 400 μm or more. The width of the first overlappingregion CA1 or the second overlapping region CA2 may be smaller than thewidth of the bending area BA. For example, the widths of the firstoverlapping region CA1 and the second overlapping region CA2 may besmaller than the width of the bending area BA. The widths of the firstoverlapping region CA1 and the second overlapping region CA2 may becorresponding to or different from each other.

Referring to FIG. 17 to 19, the width of the first overlapping regionCA1 may be equal to that of the second overlapping region CA2. Referringto FIG. 20, the width of the first overlapping region CA1 may bedifferent from the width of the second overlapping region CA2. The widthof the first overlapping region CA1 may be smaller than the width of thesecond overlapping region CA2.

A side surface 411S of the lower protective layer 411 may have variouscross-sectional shapes. The side surface 411S of the lower protectivelayer 411 may include an inclined surface or a vertical surface.Referring to FIGS. 12 and 16, the side surface 411S of the lowerprotective layer 411 may include a first inclined surface. As a result,a contact area of the lower protective layer 411 with the second platinglayer 320 may be increased, and thus removal of the lower protectivelayer 411 may be prevented.

The side surface 411S of the lower protective layer 411 may include acurved first inclined surface. For example, the inclination angle of theside surface 411S of the lower protective layer 411 with respect to thefirst plating layer 310 may be increased as the side surface 411Sbecomes closer to the first plating layer 310. The side surface 411S ofthe lower protective layer 411 may have or be at an acute angle withrespect to the first plating layer 310.

Alternatively, referring to FIGS. 14 and 18, the side surface 411S ofthe lower protective layer 411 may include a first inclined surface. Theside surface 411S of the lower protective layer 411 may include astraight first inclined surface. For example, the inclination angle ofthe side surface 411S of the lower protective layer 411 with respect tothe first plating layer 310 may be constant regardless of distance fromthe first plating layer 310. The side surface 411S of the lowerprotective layer 411 may have or be at an acute angle with respect tothe first plating layer 310.

Alternatively, referring to FIGS. 15 and 19, the side surface 411S ofthe lower protective layer 411 may include a vertical surface. The sidesurface 411S of the lower protective layer 411 may include a straightfirst inclined surface. For example, the inclination angle of the sidesurface 411S of the lower protective layer 411 with respect to the firstplating layer 310 may be at 90 degrees or the like.

Alternatively, referring to FIGS. 16 and 20, the side surface 411S ofthe lower protective layer 411 may include a vertical surface. The sidesurface 411S of the lower protective layer 411 may include a straightfirst inclined surface. For example, the inclination angle of the sidesurface 411S of the lower protective layer 411 with respect to the firstplating layer 310 may be at 90 degrees or the like. A corner 411 e thatconnects an upper surface and a side surface of the lower protectivelayer 411 may have a curvature. Accordingly, the upper surface of thelower protective layer 411 may be connected to the side surface thereofwith a curved surface. Since the lower protective layer 411 may havestrong adhesiveness, an inclined surface and/or an edge may have acurvature, thereby having a round shape.

The first inclined surface of the lower protective layer 411 may be incontact with a side surface of the first plating layer and a sidesurface of the second plating layer. The first inclined surface may beprovided in the bending area BA or the non-bending area NBA.

A thickness T3 of the lower protective layer 411 may be larger than athickness T2 of the second plating layer 320. Accordingly, the uppersurface of the lower protective layer 411 may be provided higher thanthe upper surface of the second plating layer 320. The upper surface ofthe lower protective layer 411 may be provided higher than the uppersurface of the second plating layer 320, and thus the lower protectivelayer 411 may have a step with the second plating layer 320.

The thickness T3 of the lower protective layer 411 in the bending areaBA may be 1 μm to 20 μm. For example, the thickness T3 of the lowerprotective layer 411 in the bending area BA may be 5 μm to 20 μm.

Referring to FIG. 17 to 20, the thickness T3 of the lower protectivelayer 411 in the bending area BA may be different from the thickness ofthe lower protective layer 411 in the non-bending area NBA. Thethickness of the lower protective layer 411 in the open area may belarger than the thickness of the lower protective layer 411 on the firstoverlapping region CA1. The thickness of the lower protective layer 411on the open area may be larger than the thickness of the lowerprotective layer 411 on the second overlapping region CA2.

The lower protective layer 411 may be integrally formed. Accordingly,removal of the lower protective layer 411 may be prevented, and thusreliability of the flexible circuit board may be improved. When theflexible circuit board is bent, stress due to tension may be dispersedentirely in the lower protective layer 411 integrally formed, and thusreliability may be improved. The efficiency of the process of formingthe flexible circuit board may be improved.

The upper protective layer 412 may cover the lower protective layer 411and the second plating layer 320, and may be provided wider than thelower protective layer 411. The upper protective layer 412 may beprovided to cover the upper surface of the lower protective layer 411.For example, the upper protective layer 412 may have a larger width thanthe width of the bending area BA. One surface and another surfaceopposite to the one surface of the upper protective layer 412 may beprovided on an area NBA other than the bending area BA. The upperprotective layer 412 may be provided entirely on the lower protectivelayer 411, and may be provided on the second plating layer 320 locatedin a peripheral region thereof. Accordingly, the upper protective layer412 may relieve stress concentration at an interface between the lowerprotective layer 411 and the second plating layer 320. Occurrences ofremoval of a film or crack that may occur during bending of the flexiblecircuit board may be reduced. However, the embodiment is not limitedthereto, and the upper protective layer 412 may have a widthcorresponding to the bending area BA or may have a width smaller thanthe bending area BA.

The upper protective layer 412 may be in contact with the upper surfacesof the lower protective layer 411 and the second plating layer 320. Theupper protective layer 412 may be in contact with the upper surface ofthe lower protective layer 411 on the area corresponding to the bendingarea BA and the upper surface of the second plating layer 320 on thenon-bending area NBA.

The upper protective layer 412 may entirely cover the upper surface ofthe lower protective layer 411. The upper protective layer 412 mayprevent, for example, moisture and foreign matters from infiltratinginto an interface between the lower protective layer 411 and the platinglayer 300. Therefore, damage or removal of the wiring pattern layer 200due to oxidation may be prevented.

The upper protective layer 412 may be provided on the entire uppersurface of the lower protective layer 411 and the upper surface of thesecond plating layer 320 on the non-bending area NBA by extending fromthe bending area BA on the lower protective layer 411. Accordingly, theupper protective layer 412 may prevent foreign matters from infiltratingdue to unevenness of the interface between the lower protective layer411 and the plating layer 300. Therefore, reliability and lifetime ofthe flexible circuit board may be improved.

The upper protective layer 412 may include an overlapping regioncontacting the second plating layer 320. The upper protective layer 412may overlap the second plating layer 320 on the bending area BA and/orthe non-bending area NBA.

A third overlapping region CA3 and a fourth overlapping region CA4 maybe regions in which the second plating layer 320 and the upperprotective layer 412 may be in contact with each other. The secondplating layer 320 may include a second pattern plating layer 321 and asecond pattern plating layer 322 spaced apart from each other by asecond open area OA2. The third overlapping region CA3 may be a regionin which the second pattern plating layer 321 and the upper protectivelayer 412 may be in contact with each other, and the fourth overlappingregion CA4 may be a region in which the second pattern plating layer 322and the upper protective layer 412 may be in contact with each other.

A width of the third overlapping region CA3 or the fourth overlappingregion CA4 may be 400 μm or more. The width of the third overlappingregion CA3 or the fourth overlapping region CA4 may be larger than,corresponding to, or less than the width of the bending area BA.

The widths of the overlapping regions CA3 and CA4 may be larger than asum (T1+T2) of the thicknesses of the first plating layer 310 and thesecond plating layer 320. The widths of the third overlapping region CA3and the fourth overlapping region CA4 may be larger than the sum of thethickness T1 of the first plating layer 310 and the thickness T2 of thesecond plating layer 320.

Since the upper protective layer 412 may be provided on the uppersurface of the lower protective layer 411 and on one region of the uppersurface of the second plating layer 320, adhesive strength may beincreased, thereby improving reliability of the flexible circuit board.The widths of the overlapping regions CA3 and CA4 of the upperprotective layer 412 may be larger than at least the thickness of theplating layer 300. Therefore, the flexible circuit board may preventdamage due to deformation caused by tension or compression. The widthsof the third overlapping region CA3 and the fourth overlapping regionCA4 may be corresponding to or different from each other. The upperprotective layer 412 may prevent the lower protective layer 411 frombeing removed, thereby improving reliability of the flexible circuitboard.

A side surface 412 s of the upper protective layer 412 may have variouscross-sectional shapes. The side surface 412 s of the upper protectivelayer 412 may include an inclined surface or a vertical surface.

For example, referring to FIG. 13 and FIG. 17, the side surface 412 s ofthe upper protective layer 412 may include a second inclined surface.The side surface 412 s of the upper protective layer 412 may include acurved second inclined surface. The inclination angle of the sidesurface 412 s of the upper protective layer 412 with respect to thesecond plating layer 320 may be increased as the side surface 412 sbecomes closer to the second plating layer 320. The side surface 412 sof the upper protective layer 412 may have or be at an acute angle withrespect to the second plating layer 320.

Alternatively, referring to FIG. 14 and FIG. 18, the side surface 412 sof the upper protective layer 412 may include a second inclined surface.The side surface 412 s of the upper protective layer 412 may include astraight second inclined surface. The inclination angle of the sidesurface 412 s of the upper protective layer 412 with respect to thesecond plating layer 320 may be constant regardless of distance from thesecond plating layer 320. The side surface 412 s of the upper protectivelayer 412 may have or be at an acute angle with respect to the secondplating layer 320.

Alternatively, referring to FIG. 15 and FIG. 19, the side surface 412 sof the upper protective layer 412 may include a vertical surface. Theside surface 412 s of the upper protective layer 412 may include astraight second inclined surface. For example, the inclination angle ofthe side surface 412 s of the upper protective layer 412 with respect tothe second plating layer 320 may be at 90 degrees or the like.

Alternatively, referring to FIG. 16 and FIG. 20, the side surface 412 sof the upper protective layer 412 may include a vertical surface. Theside surface 412 s of the upper protective layer 412 may include astraight second inclined surface. The inclination angle of the sidesurface 412 s of the upper protective layer 412 with respect to thesecond plating layer 320 may have or be at 90 degrees or the like. Acorner 412 e connecting an upper surface and a side surface of the upperprotective layer 412 may have a curvature. Accordingly, the uppersurface of the upper protective layer 412 may be connected to the sidesurface thereof with a curved surface.

A shape of the inclined surface of the lower protective layer 411 maycorrespond to a shape of the inclined surface of the upper protectivelayer 412. However, the embodiment is not limited thereto, and the sidesurfaces of the lower protective layer 411 and the upper protectivelayer 412 may have different structures or shapes or differentcurvatures. Since the upper protective layer 412 may have strongadhesiveness, an inclined surface and/or an edge may have a curvature,thereby having a round shape.

The second inclined surface of the upper protective layer 412 may beprovided on the second plating layer 320. The second inclined surface ofthe upper protective layer 412 may be provided on the non-bending areaNBA. However, the embodiment is not limited thereto, and the secondinclined surface of the upper protective layer 412 may be provided onthe bending area BA or on a boundary region between the bending area BAand the non-bending area NBA.

A thickness T4 of the upper protective layer 412 may be larger than thethickness T3 of the lower protective layer 411. Accordingly, an uppersurface of the upper protective layer 412 may be provided higher than anupper surface of the lower protective layer 411. Since the upper surfaceof the upper protective layer 412 is provided higher than the uppersurface of the lower protective layer 411, the lower protective layer411 may have a step with the upper protective layer 412. Therefore, theupper protective layer 412 may improve an adhesion to the lowerprotective layer 411, thereby preventing moisture infiltration or thelike.

A thickness T4 of the upper protective layer 412 in the non-bending areaNBA may be larger than that of the upper protective layer 412 in thebending area BA. Alternatively, the thickness T4 of the upper protectivelayer 412 in the non-bending area NBA may correspond to the thickness ofthe upper protective layer 412 in the bending area BA. The thickness T4of the upper protective layer 412 in the non-bending area NBA may be 1μm to 20 μm. The thickness T4 of the upper protective layer 412 in thenon-bending area NBA may be 5 μm to 20 μm.

The upper protective layer 412 may be integrally formed. Accordingly,removal of the upper protective layer 412 may be prevented, and thusreliability of the flexible circuit board may be improved. When theflexible circuit board according to the embodiment is bent, stress dueto tension may be dispersed entirely in the upper protective layer 412integrally formed, and thus reliability may be improved. The efficiencyof the process of forming the flexible circuit board may be improved.

With reference to FIG. 21 to FIG. 26, a double-side flexible circuitboard according to another embodiment may include: a substrate 100having a bending area BA and a non-bending area NBA; a first wiringpattern layer 210 provided on the bending area BA and the non-bendingarea NBA on one surface of the substrate 100; a first plating layer 310provided on the first wiring pattern layer 210 and including an openarea in an area corresponding to the bending area BA; a second platinglayer 320 provided on the first plating layer 310; a first protectivelayer 410 directly contacting one surface of the first wiring patternlayer 210 exposed at the open area, a side surface of the first platinglayer 310, and a side surface of the second plating layer 320; a secondwiring pattern layer 220 provided on a bending area BA and a non-bendingarea NBA on another surface opposite to the one surface of the substrate100; a third plating layer 330 provided on the second wiring patternlayer 220; a fourth plating layer 340 provided on the third platinglayer 330; and a second protective layer 420 provided on an areacorresponding to the bending area BA on the other surface of thesubstrate 100. The first protective layer 410 may be provided higherthan an upper surface of the second plating layer 320.

At least one protective layer of the first protective layer 410 and thesecond protective layer 420 may have a thickness of 1 μm to 20 μm. Thefirst protective layer 410 may include an upper first protective layer412 and a lower first protective layer 411 provided in two layers. Anupper portion may be provided relatively far from one surface of thesubstrate 100, and a lower portion may be provided relatively close toone surface of the substrate 100.

The upper first protective layer 412 may include overlapping regions CA3and CA4 that contact the second plating layer 320, and widths of theoverlapping regions may be greater than a sum of thicknesses of thefirst plating layer 310 and the second plating layer 320. The lowerfirst protective layer 411 may be in direct contact with the sidesurface of the first plating layer 310 and the side surface of thesecond plating layer 320. The upper first protective layer 412 may be indirect contact with an upper surface of the lower first protective layer411 and an upper surface of the second plating layer 320.

A wiring pattern layer 200 may be provided on both sides of thesubstrate 100. The wiring pattern layer 200 may include the first wiringpattern layer 210 and the second wiring pattern layer 220. The firstwiring pattern layer 210 may be provided on one surface of the flexiblesubstrate 100, and the second wiring pattern layer 220 may be providedon the other surface opposite to the one surface of the flexiblesubstrate 100.

A thickness of the first wiring pattern layer 210 may correspond to athickness of the second wiring pattern layer 220. The thicknesses of thefirst wiring pattern layer 210 and the second wiring pattern layer 220may be 1 μm to 20 μm, respectively. The first plating layer 310 may beprovided on the first wiring pattern layer 210. The third plating layer330 may be provided on the second wiring pattern layer 220.

At least one of the first plating layer 310 and the third plating layer330 may include a first open area OA1. For example, referring to FIG. 21to FIG. 23, the first plating layer 310 and the third plating layer 330may include the first open area OA1, respectively. The first platinglayer 310 may include the first open area OA1, and the third platinglayer 330 may include the first open area OA1.

Referring to FIG. 24 to FIG. 26, one of the first plating layer 310 andthe third plating layer 330 may include the first open area OA1. Thefirst plating layer 310 may include the first open area OA1.

At least one of the second plating layer 320 and the fourth platinglayer 340 may include a second open area OA2. Referring to FIGS. 21 to25, the second plating layer 320 and the fourth plating layer 340 mayinclude the second open area OA2, respectively. The second plating layer320 may include the second open area OA2, and the fourth plating layer340 may include the second open area OA2.

Referring to FIG. 26, one of the second plating layer 320 and the fourthplating layer 340 may include the second open area OA2. The secondplating layer 320 may include the second open area OA2. The secondprotective layer 420 provided on the other surface of the substrate mayinclude one or more layers.

Referring to FIG. 21 to FIG. 23 and FIG. 25, the second protective layer420 provided on the other surface of the substrate 100 may be providedin two layers. The second protective layer 420 may include an uppersecond protective layer 422 and a lower second protective layer 421. Anupper portion may be provided on a relatively far distance from theother surface of the substrate 100, and a lower portion may be providedrelatively close to the other surface of the substrate 100. The uppersecond protective layer 422 may be in direct contact with the uppersurfaces of the lower second protective layer 421 and the fourth platinglayer 340.

Referring to FIG. 21 to FIG. 23, the open area on one surface of thesubstrate 100 may be overlapped upward and downward with the open areaon the other surface of the substrate 100. Each of the open areasprovided on both sides of the substrate 100 may occupy a same region ofthe substrate 100. Each open area provided on either side of thesubstrate 100 may be located at least in part of a bending area BA, andmay include a portion that overlaps in whole or in part.

Referring to FIG. 23, the third plating layer 330 and the fourth platinglayer 340 may include an open area in areas corresponding to the bendingarea BA, and the second protective layer 420 may contact one surface ofthe second wiring pattern layer 220. The lower second protective layer421 may be in contact with one surface of the second wiring patternlayer 220.

Referring to FIG. 21 to FIG. 23, the lower second protective layer 421may be in contact with an upper surface of the second wiring patternlayer 220, a side surface of the third plating layer 330, and a sidesurface of the fourth plating layer 340. Referring to FIG. 21, the lowerfirst protective layer 411 and the lower second protective layer 421 maybe provided in the bending area. A width W1 of the first open area OA1may correspond to a width W1 of the second open area OA2.

Alternatively, referring to FIG. 22 to FIG. 23, a part of the lowersecond protective layer 421 may be in contact with the upper surface ofthe third plating layer 330 in the non-bending area NBA. A part of thelower first protective layer 411 may extend from the bending area BA tocover an upper part of the first plating layer 310. A part of the lowersecond protective layer 421 may extend from the bending area BA to coveran upper part of the third plating layer 330. At this point, a width W1a of the first open area OA1 of the first plating layer 310 may bedifferent from a width W1 b of the second open area OA2 of the secondplating layer 320. The width W1 a of the first open area OA1 of thefirst plating layer 310 may be smaller than the width W1 b of the secondopen area OA2 of the second plating layer 320.

Referring to FIG. 22, the width W1 a of the first open area OA1 of thefirst plating layer 310 may correspond to the width of the first openarea OA1 of the third plating layer 330. The width W1 b of the secondopen area OA2 of the second plating layer 320 may correspond to thewidth of the second open area OA2 of the fourth plating layer 340.

Referring to FIG. 23, the width W1 a of the first open area OA1 of thefirst plating layer 310 may be different from a width W1 c of the firstopen area OA1 of the third plating layer 330. The width W1 a of thefirst open area OA1 of the first plating layer 310 may be larger thanthe width W1 c of the first open area OA1 of the third plating layer330. The width W1 b of the second open area OA2 of the second platinglayer 320 may correspond to the width of the second open area OA2 of thefourth plating layer 340.

Referring to FIG. 25, the lower second protective layer 421 may beprovided on the third plating layer 330, and the lower second protectivelayer 421 may be provided on the upper surface of the third platinglayer 330 and the side surface of the fourth plating layer 340.

Referring to FIG. 24 and FIG. 26, the second protective layer 420provided on the other surface of the substrate 100 may be a singlelayer. Referring to FIG. 24, the second protective layer 420 may be incontact with one surface of the third plating layer 330. Referring toFIG. 26, the second protective layer 420 may be in contact with onesurface of the fourth plating layer 340.

A double-sided flexible printed circuit board may include two layers ofan upper first protective layer and a lower first protective layer onone surface of the substrate, and may include a second protective layerof a single layer on the other surface of the substrate, therebyrelieving stress during bending. The one surface of the substrateincluding the upper first protective layer and the lower firstprotective layer may be in a direction in which tensile force isapplied.

Alternatively, the double-sided flexible printed circuit board mayinclude two layers of an upper first protective layer and a lower firstprotective layer on one surface of the substrate, and may include twolayers of an upper second protective layer and a lower second protectivelayer on the other surface of the substrate, thereby relieving stressduring of bending. The one surface of the substrate including the upperfirst protective layer and the lower first protective layer may be in adirection in which tensile force is applied. Accordingly, two differentprotective layers may prevent cavities and disperse stress at aninterface. On one surface of the substrate to which a large tensileforce is applied, the width of the open area may be larger than theother surface, and thus, stress may be relieved efficiently.

For example, referring to FIG. 20, FIG. 21, FIG. 22, and FIG. 24, theupper second protective layer 422 may cover an upper surface of thelower second protective layer 421 and the fourth plating layer 340, andmay be provided wider than the lower second protective layer 421. Theone surface of the substrate including an upper first protective layerand a lower first protective layer may be in a direction in which atensile force is applied, or the other surface of the substrateincluding an upper second protective layer and a lower second protectivelayer may be in a direction in which a tensile force is applied. Thatis, regardless of a direction of bending, the embodiment may includedifferent two-layered protective layers, capable of preventing cavitiesand dispersing stress at the interface.

At least one of the first protective layer 410 and the second protectivelayer 420 may be in contact with the wiring pattern layer. For example,referring to FIG. 21 to FIG. 23, the lower first protective layer 411may be in contact with the first wiring pattern layer 210, and the lowersecond protective layer 421 may be in contact with the second wiringpattern layer 220, respectively. The lower first protective layer 411 orthe lower second protective layer 421 may be bent in a direction toreceive a tensile force.

Accordingly, as one surface of the lower first protective layer 411 orone surface of the lower second protective layer 421 may be in contactwith the wiring pattern layer, it may be possible to prevent a crackfrom being generated in the first or second wiring pattern layer 210 or220, and/or the plating layers 310, 320, 330, and 340 at a portion withtension when the flexible circuit board is folded. Therefore,reliability of the flexible circuit board may be improved. A surfacehaving a larger contact area with the wiring pattern layer between onesurface of the lower first protective layer 411 and one surface of thelower second protective layer 421 may be bent in a direction to receivea tensile force, and thus, the protective layer may relieve the tensileforce, and cracking of the wiring pattern layer may be prevented.

For example, referring to FIG. 23 to FIG. 25, one protective layer ofthe lower first protective layer 411 and the lower second protectivelayer 421 may be in contact with the wiring pattern layer 200. The lowerfirst protective layer 411 may be in contact with the wiring patternlayer 200. The lower first protective layer 411 may receive a tensileforce, and the lower second protective layer 421 may be bent in adirection to receive a compressive force. Accordingly, as one surface ofthe lower first protective layer 411 may be in contact with the firstwiring pattern layer 210, it may be possible to prevent a crack frombeing generated in the first wiring pattern layer 210 and the platinglayer 300 at a portion with tension when the flexible circuit board isfolded. Therefore, reliability of the flexible circuit board accordingto the embodiment may be improved.

A thickness of the lower first protective layer 411 may correspond to ormay be different from a thickness of the lower second protective layer421. The thickness of the first protective layer 411 may be ameasurement at the bending area BA. For example, referring to FIG. 21 toFIG. 23, the thickness T3 of the lower first protective layer 411 may bedifferent from the thickness T3 of the lower second protective layer421, The thickness of the lower first protective layer 411 may be 1 μmto 20 μm, and the thickness of the lower second protective layer 421 maybe 1 μm to 20 μm.

The lower first protective layer 411 and the lower second protectivelayer 421 may be in contact with the first and second wiring patternlayers 210 and 220, respectively. The thickness of the lower firstprotective layer 411 may be 10 μm to 20 μm. The thickness of the lowersecond protective layer 421 may be 5 μm to 15 μm. The lower firstprotective layer 411 may receive a tensile force, and the lower secondprotective layer 421 may be bent in a direction to receive a compressiveforce. Since the lower first protective layer 411 receiving a tensileforce has a larger thickness than the lower second protective layer 421receiving a compressive force, it may be possible to prevent a crackfrom being generated in the first wiring pattern layer 210, and/or theplating layers 310 and 320 at a portion with tension when the flexiblecircuit board is folded. Therefore, reliability of the flexible circuitboard may be improved.

For example, referring to FIG. 24 to FIG. 26, a thickness T3 a of thelower first protective layer 411 may be different from a thickness T3 bof the lower second protective layer 421. The thickness T3 a of thelower first protective layer 411 may be larger than the thickness T3 bof the lower second protective layer 421. The thickness of the lowerfirst protective layer 411 may be 10 μm to 20 μm, and the thickness ofthe lower second protective layer 421 may be 5 μm to 15 μm. The lowerfirst protective layer 411 may receive a tensile force, and the lowersecond protective layer 421 may be bent in a direction to receive acompressive force. Since the lower first protective layer 411 receivinga tensile force has a larger thickness than the lower second protectivelayer 421 receiving a compressive force, it may be possible to prevent acrack from being generated in the first wiring pattern layer 210, and/orthe plating layers 310 and 320 at a portion with tension when theflexible circuit board is folded. Thus, reliability of the flexiblecircuit board may be improved.

Referring to FIG. 22 and FIG. 23, a first overlapping region and asecond overlapping region in which the first plating layer and the firstprotective layer may be in contact with each other may be included. Awidth of the first overlapping region may correspond to a width of thesecond overlapping region.

Referring to FIG. 22, a width of a first overlapping region CA1 in whichthe first plating layer 310 and the lower first protective layer 411 maybe in contact with each other on one side of a first open area OA1 maycorrespond to that of a fifth overlapping region CA5 in which the thirdplating layer 330 and the lower second protective layer 421 are contactwith each other at one side of the first open area OA1. A width of asecond overlapping region CA2 in which the first plating layer 310 andthe lower first protective layer 411 may be in contact with each otheron the other side of a first open area OA1 may correspond to that of asixth overlapping region CA6 in which the third plating layer 330 andthe lower second protective layer 421 may be contact with each other atthe other side of the first open area OA1. Referring to FIG. 23, thewidth of the fifth overlapping region CA5 may be larger than the widthof the first overlapping region CA1. The width of the sixth overlappingregion CM may be larger than the width of the second overlapping regionCA2.

Referring to FIG. 21 to FIG. 26, the upper second protective layer 422may cover the lower second protective layer 421 and the fourth platinglayer 340, and may be provided wider than the lower second protectivelayer 421. The upper second protective layer 422 may cover the uppersurface of the lower second protective layer 421, and may be provided tohave a larger width than the bending area BA. One surface of the uppersecond protective layer 422 and another surface opposite to the onesurface may be provided on the non-bending area NBA. The upper secondprotective layer 422 may be provided entirely on the lower secondprotective layer 421, and may be provided on a peripheral area of thelower second protective layer 421.

The upper second protective layer 422 may be in contact with the uppersurfaces of the lower second protective layer 421 and the fourth platinglayer 340. The upper second protective layer 422 may be in contact withthe upper surface of the lower second protective layer 421 on thebending area BA and the upper surface of the fourth plating layer 340 onthe non-bending area NBA.

The upper second protective layer 422 may entirely cover the uppersurface of the lower second protective layer 421. The upper secondprotective layer 422 may prevent for example, moisture and foreignmatter from infiltrating into the interface between the lower secondprotective layer 421 and the plating layer 300. As a result, it maypossible to prevent damage or removal of the wiring pattern layer 200due to oxidation.

The upper second protective layer 422 may extend over the entire uppersurface of the lower second protective layer 421 and the bending area BAon the lower second protective layer 421, and may be provided on theupper surface of the fourth plating layer 340 on the non-bending areaNBA. Thus, the upper second protective layer 422 may prevent foreignmatters from infiltrating due to unevenness of the interface between thelower second protective layer 421 and the plating layer 300. Therefore,reliability and lifetime of the flexible circuit board may be improved.The upper second protective layer 422 may include an overlapping regioncontacting the fourth plating layer 340. The upper second protectivelayer 422 may overlap the fourth plating layer 340 on the non-bendingarea NBA.

A shape of the first protective layer 410 may be symmetrical with ashape of the second protective layer 420. For example, the lower firstprotective layer 411 and the lower second protective layer 421 may beT-shaped. Alternatively, the shape of the first protective layer 410 maybe different from the shape of the second protective layer 420. Forexample, the lower first protective layer 411 may be T-shaped, and thelower second protective layer 421 may be stripe-shaped.

Since the upper second protective layer 422 may be provided on the uppersurface of the lower second protective layer 421 and on one area of theupper surface of the fourth plating layer 340, adhesive strength may beincreased, and thus reliability of the flexible circuit board may beimproved.

The widths of the overlapping regions CA3 and CA4 between the uppersecond protective layer 422 and the fourth plating layer 340 may belarger than the thickness of the plating layer 300. Accordingly, theflexible circuit board may prevent damage due to deformation caused bytension or compression. The widths of the third overlapping region CA3and the fourth overlapping region CA4 may be corresponding to ordifferent from each other.

The upper second protective layer 422 may prevent removal of the lowersecond protective layer 421, thereby improving reliability of theflexible circuit board. An upper surface of the upper second protectivelayer 422 may be provided higher than the upper surface of the lowersecond protective layer 421. Since the upper surface of the upper secondprotective layer 422 is provided higher than the upper surface of thelower second protective layer 421, the lower second protective layer 421may have a step with the upper second protective layer 422. Accordingly,the upper second protective layer 422 may be capable of improvingadhesion to the lower second protective layer 421, and thus moistureinfiltration or the like may be prevented.

In the double-sided flexible printed circuit board according to theembodiments, the upper protective layer having a larger width than anyone of the lower first protective layer and the lower second protectivelayer may be provided higher than the upper surface of any one of thelower first protective layer and the lower second protective layer on atleast one protective layer of the lower first protective layer and thelower second protective layer. The upper first protective layer having awidth larger than that of the lower first protective layer may beprovided on the lower first protective layer, and the upper secondprotective layer having a width larger than that of the lower secondprotective layer may be provided on the lower second protective layer.Accordingly, stress generated during bending the plurality of protectivelayers on at least one surface of the substrate may be dispersed, andthus breakage of the plating layer and/or the wiring pattern layer maybe prevented.

The upper first protective layer provided on the lower first protectivelayer may block access of an infiltrable material at the interfacebetween the lower first protective layer and the plating layer, therebypreventing damage or removal of a film due to oxidation of a wiringpattern. The upper second protective layer provided on the lower secondprotective layer may block access of an infiltrable material at theinterface between the lower second protective layer and the platinglayer, thereby preventing damage or removal of a film due to oxidationof a wiring pattern.

Since the upper surface of the lower first protective layer may beprovided higher than the upper surface of the second plating layer, acavity may be prevented from being formed between the lower firstprotective layer and the plating layer or between the lower firstprotective layer and the wiring pattern layer. Therefore, removal of afilm or damage of a wiring pattern layer and/or a plating layer may beprevented. Since a protective layer on a side receiving a tensile forcemay be in contact with a wiring pattern layer, cracking and breakage ofa wiring pattern layer and/or a plating layer due to bending may beprevented, and thus reliability may be improved.

The double-sided flexible printed circuit board may include a lowerfirst protective layer 411 provided between the first plating layer 310and the second plating layer 320. The double-sided flexible printedcircuit board may include the structure of a lower first protectivelayer 411 in which a portion may be buried between the first platinglayer 310 and the second plating layer 320, and thus a tensile force ofa bending area may be buffered, and cracking of a wiring pattern layerand a plating layer may be prevented.

As at least one protective layer of the lower first protective layer andthe lower second protective layer may be in contact with the wiringpattern layer, a crack due to a change in tensile force during bendingmay be prevented. A semiconductor chip may be mounted in a narrow areaof an electronic device in high density, and a high resolution displaymay be realized. Furthermore, the embodiments may prevent appearancedefects and reliability degradation due to generation of Sn particles.

Hereinafter, a method of manufacturing a flexible circuit boardaccording to the embodiments is be described with reference to FIG. 27.The manufacturing method of a flexible circuit board according to theembodiment may include preparing a substrate having a thickness of 12 to125 μm, forming a wiring pattern layer having a thickness of 1 to 20 μmon one surface of the substrate, providing a first protective layerhaving a thickness of 1 to 20 μm on a bending area of the wiring patternlayer, forming a first plating layer having a thickness of 0.1 μm orless on an area other than an area where the first protective layer isprovided on the wiring pattern layer, providing a second plating layerhaving a thickness of 1 μm or less on the first plating layer, andproviding a second protective layer covering the first protective layerand the second plating layer and having a width larger than that of thefirst protective layer to a thickness of 1 to 20 μm.

Hereinafter, a method of manufacturing a double-sided flexible printedcircuit board is described with reference to FIGS. 28 to 31. Theembodiment is not limited thereto, and some components previouslydiscussed may be omitted during the process. For example, the uppersecond protective layer 422 may be omitted. In addition, some componentsmay be located differently during the process. For example, the lowersecond protective layer 421 may be provided on the third plating layer330, or the lower second protective layer 421 may be provided on thefourth plating layer 340.

Referring to FIG. 28, a double-sided flexible printed circuit board maybe manufactured according to a dry film masking method or a photo solderresist (PSR) printing method. First, a first wiring pattern layer 210and a second wiring pattern layer 220 may be prepared on both sides of asubstrate 100. A circuit may be formed on both surfaces of a substrate100. The substrate 100 may be a polyimide flexible substrate, and awiring pattern may include copper.

Next, an upper sacrificial layer T1 may be formed by laminating a dryfilm on the first wiring pattern layer 210 or by printing a photo solderresist layer. A lower sacrificial layer B1 may be formed by laminating adry film on the second wiring pattern layer 220 or by printing a photosolder resist layer. A mask may be provided on the upper sacrificiallayer T1 and the lower sacrificial layer B1, and an exposure step forexposing ultraviolet rays may be performed.

Next, a development step of removing the unexposed upper sacrificiallayer T1 and the lower sacrificial layer B1 may be performed.Accordingly, a patterned upper sacrificial layer P1 and a patternedlower sacrificial layer P2 may be formed. A first plating layer 310 maythen be formed in the peripheral area of the patterned upper sacrificiallayer P1. A third plating layer 330 may be formed in the peripheral areaof the patterned lower sacrificial layer P2.

Next, the patterned upper sacrificial layer P1 and the patterned lowersacrificial layer P2 may be peeled off. Accordingly, a first platinglayer 310 and a third plating layer 330 including a first open area maybe formed. Each of the first plating layer 310 and the third platinglayer 330 may be tin-plated.

Next, lower first and lower second protective layers 411 and 421covering side surfaces and parts of upper surfaces of the first platinglayer 310 and the third plating layer 330 may be provided while fillingthe first open area. Upper surfaces of the lower first and lower secondprotective layers 411 and 421 may have a larger width than that of thebending area.

Second and fourth plating layers 320 and 340 may then be formed in theperipheral area of the lower first and lower second protective layers411 and 421. The second and fourth plating layers 320 and 340 may beformed in an area where the lower first and lower second protectivelayers 411 and 421 are not provided with a thickness smaller than thatof the protective layer. Accordingly, side surfaces of the lower firstand lower second protective layers 411 and 421 may be in contact withthe second and fourth plating layers 320 and 340. The second platinglayer 320 and the fourth plating layer 340 may be tin-platedrespectively.

Next, an upper first protective layer 412 may be formed on the entireupper surface of the lower first protective layer 411 and on one area ofthe upper surface of the second plating layer 320 which may be aperipheral area of the lower first protective layer 411. An uppersurface of the upper first protective layer 412 may be formed with aheight higher than that of the lower first protective layer 411. Theupper first protective layer 412 may include a same material as amaterial of the lower first protective layer 411.

An upper second protective layer 422 may be formed on the entire uppersurface of the lower second protective layer 421 and on one area of theupper surface of the fourth plating layer 340 which may be a peripheralarea of the lower second protective layer 421. An upper surface of theupper second protective layer 422 may be formed with a height higherthan that of the lower second protective layer 421. The upper secondprotective layer 422 may include the same material as that of the lowersecond protective layer 421.

Referring to FIG. 29, a double-sided flexible printed circuit board maybe manufactured according to a PET masking method. First, a first wiringpattern layer 210 and a second wiring pattern layer 220 may be preparedon both sides of a flexible substrate 100. A circuit is formed on bothsurfaces of a flexible substrate 100. The flexible substrate 100 may bea polyimide flexible substrate, and a wiring pattern may include copper.

Next, a PET masking film may be punched to prepare a PET masking filmhaving a through-hole. A patterned upper sacrificial layer P1 may beformed by laminating a PET masking film having through holes on thefirst wiring pattern layer 210. A patterned lower sacrificial layer P2may be formed by laminating a PET masking film having through holes onthe second wiring pattern layer 220.

Next, a first plating layer 310 may be formed in a through hole of thepatterned upper sacrificial layer P1. A third plating layer 330 may beformed in a through hole of the patterned lower sacrificial layer P2.The patterned upper sacrificial layer P1 and the patterned lowersacrificial layer P2 may then be peeled off. Accordingly, a firstplating layer 310 and a third plating layer 330 including a first openarea may be formed. The first plating layer 310 and the third platinglayer 330 may be tin-plated respectively.

Next, lower first and lower second protective layers 411 and 421covering side surfaces and parts of upper surfaces of the first platinglayer 310 and the third plating layer 330 may be provided while fillingthe first open area. Upper surfaces of the lower first and lower secondprotective layers 411 and 421 may have a larger width than that of thebending area.

Second and fourth plating layers 320 and 340 may be formed in theperipheral area of the lower first and lower second protective layers411 and 421. The second and fourth plating layers 320 and 340 may beformed in an area where the lower first and lower second protectivelayers 411 and 421 are not provided with a thickness smaller than thatof the protective layer. Accordingly, side surfaces of the lower firstand lower second protective layers 411 and 421 may be in contact withthe second and fourth plating layers 320 and 340. The second platinglayer 320 and the fourth plating layer 340 may be tin-platedrespectively.

Next, an upper first protective layer 412 may be formed on the entireupper surface of the lower first protective layer 411 and on one area ofthe upper surface of the second plating layer 320 which may be aperipheral area of the lower first protective layer 411. An uppersurface of the upper first protective layer 412 may have a height higherthan that of the lower first protective layer 411. The upper firstprotective layer 412 may include the same material as that of the lowerfirst protective layer 411.

An upper second protective layer 422 may be formed on the entire uppersurface of the lower second protective layer 421 and on one area of theupper surface of the fourth plating layer 340 which may be a peripheralarea of the lower second protective layer 421. An upper surface of theupper second protective layer 422 may be formed with a height higherthan that of the lower second protective layer 421. The upper secondprotective layer 422 may include the same material as that of the lowersecond protective layer 421.

Referring to FIG. 30, a double-sided flexible printed circuit board maybe manufactured according to a photoresist (PR) printing or gravureprinting method. First, a first wiring pattern layer 210 and a secondwiring pattern layer 220 may be prepared on both sides of a flexiblesubstrate 100. A circuit may be formed on both surfaces of a flexiblesubstrate 100. The flexible substrate 100 may be a polyimide flexiblesubstrate, and a wiring pattern may include copper.

Next, a photoresist ink may be applied on the first wiring pattern layer210 to form a patterned upper sacrificial layer P1. A photoresist inkmay be printed on the second wiring pattern layer 220 to form apatterned lower sacrificial layer P2.

Next, a first plating layer 310 may be formed in the peripheral area ofthe patterned upper sacrificial layer P1. A third plating layer 330 maybe formed in the peripheral area of the patterned lower sacrificiallayer P2. The patterned upper sacrificial layer P1 and the patternedlower sacrificial layer P2 may then be peeled off. Accordingly, a firstplating layer 310 and a third plating layer 330 including a first openarea may be formed. The first plating layer 310 and the third platinglayer 330 may be tin-plated respectively.

Next, lower first and lower second protective layers 411 and 421covering side surfaces and parts of upper surfaces of the first platinglayer 310 and the third plating layer 330 may be provided while fillingthe first open area. Upper surfaces of the protective layers may have alarger width than that of the bending area.

Second and fourth plating layers 320 and 340 may be formed in theperipheral area of the lower first and lower second protective layers411 and 421. The second and fourth plating layers 320 and 340 may beformed in an area where the lower first and lower second protectivelayers 411 and 421 are not provided with a thickness smaller than thatof the protective layer. Accordingly, side surfaces of the protectivelayers may be in contact with the second and fourth plating layers 320and 340. The second plating layer 320 and the fourth plating layer 340may be tin-plated respectively.

Next, an upper first protective layer 412 may be formed on the entireupper surface of the lower first protective layer 411 and on one area ofthe upper surface of the second plating layer 320 which may be aperipheral area of the lower first protective layer 411. An uppersurface of the upper first protective layer 412 may be formed with aheight higher than that of the lower first protective layer 411. Theupper first protective layer 412 may include the same material as thatof the lower first protective layer 411.

An upper second protective layer 422 may be formed on the entire uppersurface of the lower second protective layer 421 and on one area of theupper surface of the fourth plating layer 340 which is a peripheral areaof the lower second protective layer 421. An upper surface of the uppersecond protective layer 422 may be formed with a height higher than thatof the lower second protective layer 421. The upper second protectivelayer 422 may include the same material as that of the lower secondprotective layer 421.

Referring to FIG. 31, a double-sided flexible printed circuit board maybe manufactured according to a Spurt Jar plating method. First, a firstwiring pattern layer 210 and a second wiring pattern layer 220 may beprepared on both sides of a flexible substrate 100. A circuit may beformed on both surfaces of a flexible substrate 100. The flexiblesubstrate 100 may be a polyimide flexible substrate, and a wiringpattern may include copper.

Next, a first plating layer 310 and a third plating layer 330 includinga first open area may be formed in an area corresponding to a bendingarea by performing Spurt Jar plating. The first plating layer 310 andthe third plating layer 330 may be tin-plated respectively. Protectivelayers covering side surfaces and parts of upper surfaces of the firstplating layer 310 and the third plating layer 330 may be provided whilefilling the first open area. Upper surfaces of the protective layers mayhave a larger width than that of the bending area.

Second and fourth plating layers 320 and 340 may be formed in peripheralareas of lower first and lower second protective layers 411 and 421. Thesecond and fourth plating layers 320 and 340 may be formed in an areawhere the lower first and lower second protective layers 411 and 421 arenot provided with a thickness smaller than that of the protective layer.Accordingly, side surfaces of the protective layers may be in contactwith the second and fourth plating layers 320 and 340. The secondplating layer 320 and the fourth plating layer 340 may be tin-platedrespectively.

Next, an upper first protective layer 412 may be formed on the entireupper surface of the lower first protective layer 411 and on one area ofthe upper surface of the second plating layer 320 which may be aperipheral area of the lower first protective layer 411. An uppersurface of the upper first protective layer 412 may be formed with aheight higher than that of the lower first protective layer 411. Theupper first protective layer 412 may include the same material as thatof the lower first protective layer 411.

An upper second protective layer 422 may be formed on the entire uppersurface of the lower second protective layer 421 and on one area of theupper surface of the fourth plating layer 340 which may be a peripheralarea of the lower second protective layer 421. An upper surface of theupper second protective layer 422 may be formed with a height higherthan that of the lower second protective layer 421. The upper secondprotective layer 422 may include the same material as that of the lowersecond protective layer 421.

A chip on film (COF) module 10 may include a flexible circuit board, ora flexible circuit board chip package 10, according to the embodiments.The COF module having a driving chip mounted thereon may be manufacturedby providing on the wiring pattern layer 200 the driving chip that maybe electrically connected to the wiring pattern layer 200 on theflexible circuit board.

Cross-sectional views of a flexible circuit board mounted on anelectronic device are described with reference to FIG. 32 and FIG. 33. Abent portion of a flexible circuit board mounted on the electronicdevice may be equal to, wider or narrower than the bending area BA. Anarea without a plating layer may be in at least a part of the bendingarea BA. Therefore, breakage of the plating layer during bending may beprevented. The bending area BA may be wider than, corresponding to, ornarrower than an area where the plating layer is not formed.

Referring to FIG. 32 and FIG. 33, the lower protective layer 411 may beprovided narrower than the bending area BA. Alternatively, referring toFIG. 32, the lower protective layer 411 may be provided only in thebending area BA. Referring to FIG. 32 and FIG. 34, the upper protectivelayer 412 may be provided wider than the bending area BA. Alternatively,referring to FIG. 32, the upper protective layer 412 may be providedonly in the bending area BA.

Referring to FIG. 35, the flexible circuit board according to the firstand second embodiments may be included in an electronic device. The chipon film (COF) module 10 may include providing the driving chip 40 on thenon-bending area NBA of the flexible circuit board, For example, in thebending area BA, the flexible substrate 100 may have a shape similar toa C-shape. In the bending area BA, the cross section of the flexiblesubstrate 100 may have a curve shape. The bending area BA may be an areawhere one surface is bending and facing one surface of the substrate100, or an area where the other surface faces the other surface of thesubstrate 100.

In the non-bending area NBA, the flexible substrate 100 may have a shapesimilar to a plate shape. In the non-bending area NBA, the cross sectionof the flexible substrate 100 may have a straight shape. The non-bendingarea NBA may include an area where the substrate 100 may be partiallybent to connect with a display panel or a separate circuit board. Thenon-bending area NBA may be an area where one surface of the substratemay not face one opposite surface.

The bending area BA may be provided between the non-bending areas NBA.The bending area BA may be bent to connect the flexible circuit board toa display panel and a printed circuit board. The cross-sectional area ofthe bending area BA may be smaller than that of the non-bending areaNBA. Accordingly, the flexible circuit board may be provided between thedisplay panel and the printed circuit board.

The COF module 10 may be located between a display panel 20 and aprinted circuit board 30 to connect an electrical signal. The printedcircuit board 30 may be a rigid printed circuit board or a flexibleprinted circuit board. One end of the COF module 10 including theflexible circuit board may be electrically connected by being in contactwith the display panel 20, and another end opposite to the one end maybe electrically connected by being in contact with the printed circuitboard 30. Such contact may be a direct contact. Alternatively, thecontact may be a contact with an anisotropic conductive film (ACF)therebetween.

For example, the ACF may be provided between the COF module 10 and theprinted circuit board 30. The COF module 10 and the printed circuitboard 30 may be bonded together and electrically connected by the ACFsimultaneously. The ACF may be a resin in which conductive particles maybe dispersed. Therefore, an electrical signal connected by the printedcircuit board 30 may be transmitted to the COF module 10 through theconductive particles contained in the ACF.

The flexible circuit board 10 may be connected to the display panel 20in a first bonding area A1. The flexible circuit board 10 may beconnected to the printed circuit board 30 in a second bonding area A2.The first bonding area A1 and the second bonding area A2 may be one endor another end of a non-bending area NBA.

A bending area BA that may be bent between the first bonding area A1where the flexible circuit board 10 may be connected to the displaypanel 20 and the second bonding area A2 where the flexible circuit board10 may be connected to the printed circuit board 30 may be located.

Since the COF module 10 may include a flexible substrate, the COF module10 may have a rigid shape or a bending shape between the display panel20 and the printed circuit board 30. The COF module 10 may be bent andconnected between the display panel 20 and the printed circuit board 30provided opposite to each other, and thus a thickness of the electronicdevice may be reduced, and a degree of freedom of design may beimproved. The COF module 10 including the flexible substrate 100 may notbreak the wiring even in curved form, and thus reliability of theelectronic device including the COF module may be improved.

FIG. 36 and FIG. 37 are cross-sectional views of a chip package that mayinclude a double-sided flexible printed circuit board according to anembodiment. Referring to FIG. 36 and FIG. 37, the substrate 100 mayinclude a through hole. The substrate 100 may include a plurality ofthrough holes. The plurality of through holes of the substrate 100 maybe formed individually or simultaneously by a mechanical process or achemical process. For example, the plurality of through holes of thesubstrate 100 may be formed by a drilling process or an etching process.The through holes of the substrate may be formed through laser punchingand desmearing processes. The desmearing process may be a process ofremoving a polyimide smear attached to an inner surface of the throughhole. By the desmearing process, an inner surface of the polyimidesubstrate may have an inclined surface similar to a straight line.

Wiring pattern layers 210 and 220, plating layers 300: 310, 320, 330 and340, and protective layers 410 and 420 may be provided on the substrate100. The wiring pattern layers 210 and 220, plating layers 310, 320,330, and 340, and protective layers 410 and 420 may be sequentiallyprovided on both surfaces of the substrate 100.

A conductive pattern part CP may be provided on one surface or bothsurfaces of the substrate 100. The conductive pattern part CP mayinclude a wiring pattern layer and a plating layer. The wiring patternlayers 210 and 220 may be formed by at least one method of evaporation,plating, and sputtering. For example, a wiring layer for forming acircuit may be formed by electrolytic plating after sputtering. A wiringlayer for forming a circuit may be a copper plating layer formed byelectroless plating. Alternatively, the wiring layer may be a copperplating layer formed by electroless plating and electrolytic plating. Apatterned wiring layer may be formed on both surfaces of a flexiblecircuit board, that is, on the upper and lower surfaces, afterlaminating a dry film on the wiring layer, through the processes ofexposure, development, and etching. Thus, the wiring pattern layers 210and 220 may be formed.

Conductive materials may be filled in via holes V1, V2, and V3 passingthrough the substrate 100. The conductive material filled in a via holemay correspond to the wiring pattern layers 210 and 220, or may bedifferent conductive materials. For example, the conductive materialfilled in a via hole may include at least one metal among copper (Cu),aluminum (Al), chromium (Cr), nickel (Ni), silver (Ag), molybdenum (Mo),gold (Au), titanium (Ti), and an alloy thereof. The electrical signal ofthe conductive pattern part CP on the upper surface of the substrate 100may be transmitted to the conductive pattern part CP of the lowersurface of the substrate 100 through the conductive material filled in avia hole.

A plating layer 300 may be formed on the wiring pattern layers 210 and220. Thereafter, a protective part PP may be screen printed on theconductive pattern part CP. Referring to FIG. 36, the area of the wiringpattern layer 210 and 220 may correspond to or differ from the platinglayer 300. The area of the first plating layer 310 may correspond to orbe different from the area of the second plating layer 320. The area ofthe first wiring pattern layer 210 may correspond to that of the platinglayer 300. The area of the first plating layer 310 may correspond to thearea of the second plating layer 320.

The first plating layer 310 may be provided on the first wiring patternlayer 210, and the second plating layer 320 may be formed on the firstplating layer 310, and the first protective layer 410 may be partiallyprovided on the second plating layer 320. Referring to FIG. 37, the areaof the wiring pattern layers 210 and 220 may be different from that ofthe plating layer 300. The area of the first wiring pattern layer 210may correspond to the area of the first plating layer 310. The area ofthe first plating layer 310 may be different from that of the secondplating layer 320. For example, the area of the first plating layer 310may be larger than that of the second plating layer 320.

The first plating layer 310 may be provided on the first wiring patternlayer 210, and the protective layer 410 may be partially provided on thefirst plating layer 310. The second plating layer 320 may be provided onan area on the first plating layer 310 other than an area where theprotective layer 410 is provided.

The first plating layer 310 in contact with a lower surface of theprotective layer 410 may be an alloy layer of copper and tin. The secondplating layer 320 contacting a side surface of the protective layer 410may include pure tin. As a result, formation of a cavity part betweenthe protective layer 410 and the first plating layer 310 may prevent theprotective layer from being removed and prevent the formation ofwhiskers, thereby increasing adhesion of the protective layer.Therefore, the embodiments may include two layers of plating layers, andthus an electronic device with high reliability may be provided.

The driving chip 40, the display panel 20, and the printed circuit board30 mounted on the flexible circuit board chip package may be connected.The flexible circuit board chip package 10 may include a substrate 100including a through hole, wiring pattern layers 210 and 220 provided onboth sides of the substrate including a through hole, a first or thirdplating layer 310 or 330 provided on the wiring pattern layer, secondand fourth plating layers 320 and 340 provided on the first or thirdplating layer, and protective layers 410 and 420 partially provided onthe wiring pattern layers.

A providing area of the protective layer 400 on which the protectivelayer 400 may be formed may be the protective part PP. The conductivepattern part CP may be exposed to the outside in areas NPA1 and NPA3other than the protective part where the protective layer is not formed.The conductive pattern part CP may be electrically connected to thedriving chip 40, the display panel 20, and the printed circuit board 30in an area where a protective part is not provided on an open area of aprotective layer or a conductive pattern part.

A lead pattern part and a test pattern part of the flexible circuitboard chip package 10 may not overlap a protective part PP. The leadpattern part and the test pattern part may be a conductive pattern partlocated in an open area not covered by a protective layer, and may bedistinguished into a lead pattern part and a test pattern part accordingto functions.

The lead pattern part may be a conductive pattern part to be connectedto the driving chip, the display panel, or the printed circuit board.The test pattern part may be a conductive pattern part for checkingwhether a flexible circuit board and a product of a chip packageincluding the same may be defective.

The lead pattern part may be distinguished into an inner lead patternpart and an outer lead pattern part depending on a location. One area ofa conductive pattern part that may be relatively close to the drivingchip and not overlapped by a protective layer may be represented as theinner lead pattern part. One area of a conductive pattern part that maybe located relatively far from the driving chip and not overlapped by aprotective layer may be represented as the outer lead pattern part.

Referring to FIG. 36 to FIG. 39, the substrate 100 may include a firstinner lead pattern part I1, a second inner lead pattern part I2, a thirdinner lead pattern part I3, and a fourth inner lead pattern part I4. Thesubstrate 100 may include a first outer lead pattern part O1, a secondouter lead pattern part O2, a third outer lead pattern part O3, and afourth outer lead pattern part O4. The substrate 100 may include a firsttest pattern part T1 and a second test pattern part T2.

The first inner lead pattern part I1, the second inner lead pattern partI2, the third inner lead pattern part I3, the first outer lead patternpart O1, and the second outer lead pattern part O2 may be provided onone surface of the substrate 100. The fourth inner lead pattern part I4,the third outer lead pattern part O3, the fourth outer lead pattern partO4, the first test pattern part T1, and the second test pattern part T2may be included on another surface of the substrate 100 opposite to theone surface.

The driving chip 40, which may be provided on one surface of thesubstrate 100 may be connected to the first inner lead pattern part I1,the second inner lead pattern part I2, or the third inner lead patternpart I3 through a first connecting part 70. The first connecting part 70may include a first sub first connecting part 71, a second sub firstconnecting part 72, and a third sub first connecting part 73 dependingon location and/or function. The driving chip 40 provided on one surfaceof the substrate 100 may be electrically connected to the first innerlead pattern part I1 through the first sub first connecting part 71.

The first inner lead pattern part I1 may transmit an electrical signalto the first outer lead pattern part O1 adjacent to a second via hole V2along the upper surface of the substrate 100. The second via hole V2 andthe first outer lead pattern part O1 may be electrically connected toeach other. The first inner lead pattern part I1 and the first outerlead pattern part O1 may be one end and another end of the conductivepattern part extending in one direction.

For example, the printed circuit board 30 may be connected to the firstouter lead pattern part O1 through an adhesive layer 50. Accordingly, asignal transmitted from the first chip may be transmitted to the printedcircuit board 30 through the first inner lead pattern part I1 and thefirst outer lead pattern part O1.

The first inner lead pattern part I1 may be electrically connected tothe second via hole V2 along the upper surface of the substrate 100, andan electrical signal may be transmitted to the third outer lead patternpart O3 adjacent to the second via hole V2 along the lower surface ofthe substrate 100 through the conductive material filled in the secondvia hole V2. The second via hole V2 may be electrically connected to thethird outer lead pattern part O3. Accordingly, the printed circuit board30 may be electrically connected to the third outer lead pattern part O3through the adhesive layer 50.

The driving chip 40 provided on one surface of the substrate 100 may beelectrically connected to the second inner lead pattern part I2 throughthe second sub first connecting part 72. The second inner lead patternpart I2 provided on the upper surface of the substrate 100 may transmitan electrical signal to the fourth inner lead pattern part I4 and thefirst test pattern part T1 adjacent to a first via hole VI along thelower surface of the substrate 100 through a conductive material filledin the first via hole V1 located under the second inner lead patternpart I2. The first via hole V1, the first test pattern part T1, and thefourth inner lead pattern part I4 may be electrically connected on thelower surface of the substrate. The display panel 20 may be attached tothe fourth inner lead pattern part I4 and the fourth outer lead patternpart O4.

The first test pattern part T1 may confirm a failure of an electricalsignal that may be transmitted through the first via hole V1. Forexample, accuracy of a signal transmitted to the fourth inner leadpattern part I4 may be confirmed through the first test pattern part T1.By measuring a voltage or a current in the first test pattern part T1,it may be possible to confirm whether a short circuit or a short occursor a generated location of the short circuit or short in the conductivepattern part located between the first chip and the display panel,thereby improving product reliability.

The driving chip 40 provided on one surface of the substrate 100 may beelectrically connected to the third inner lead pattern part I3 throughthe third sub first connecting part 73. The third inner lead patternpart I3 may transmit an electrical signal to the second outer leadpattern part O2 adjacent to a third via hole V3 along the upper surfaceof the substrate 100. The third via hole V3 and the second outer leadpattern part O2 may be electrically connected. The third inner leadpattern part I3 and the second outer lead pattern part O2 may be one endand the other end of the conductive pattern part extending in onedirection.

The third inner lead pattern part I3 may be electrically connected tothe third via hole V3 along the upper surface of the substrate 100, andan electrical signal may be transmitted to the fourth outer lead patternpart O4 and the second test pattern part T2 adjacent to the third viahole V3 along the lower surface of the substrate 100 through theconductive material filled in the third via hole V3.

The second via hole V2, the fourth outer lead pattern part O4, and thesecond test pattern part T2 may be electrically connected at the lowersurface of the substrate. As described above, the display panel 20 maybe attached to the fourth inner lead pattern part I4 and the fourthouter lead pattern part O4 through the adhesive layer 50.

The second test pattern part T2 may confirm a failure of an electricalsignal that may be transmitted through the third via hole V3. Forexample, accuracy of a signal transmitted to the fourth outer leadpattern part O4 may be confirmed through the second test pattern partT2. By measuring a voltage or a current in the second test pattern partT2, it may be possible to confirm whether a short circuit or a shortoccurs or a generated location of the short circuit or short in theconductive pattern part located between the first chip and the displaypanel, thereby improving product reliability.

The flexible circuit board may dispose or have the display panel 20 onthe other surface opposite to one surface on which the driving chip 40is provided, thereby improving a degree of freedom of design.

FIG. 38 is a top plan view of the double-sided flexible printed circuitboard according to FIG. 37, and FIG. 39 is a bottom view of thedouble-sided flexible printed circuit board according to FIG. 37.Referring to FIG. 38 and FIG. 39, the substrate 100 may have sprocketholes on both sides in the longitudinal direction for convenience ofmanufacturing or processing. Accordingly, the substrate 100 may berolled or unwound by sprocket holes SH in a roll-to-roll manner.

The substrate 100 of the embodiment may be defined as an inner area IRand an outer area OR based on a cut portion indicated by a dotted line.The outer area OR may include a plurality of sprocket holes SH and aplurality of dummy patterns DP. The sprocket holes SH may improve theconvenience of transporting a flexible circuit board.

A dummy area DR may be included between the sprocket holes SH and theinner area IR in which a conductive pattern part CP may be provided. Aplurality of dummy patterns DP may be provided in the dummy area DR. Theplurality of dummy patterns DP of the outer area OR may prevent theconductive pattern part CP of the inner area IR from being excessivelyetched and, and thus uniformity of the width and pitch of the conductivepattern part CP may be improved.

The conductive pattern part for connecting the driving chip, the displaypanel, and the printed circuit board may be provided in the inner areaIR of the substrate 100. By cutting a portion where a sprocket hole isformed on the substrate 100 and providing a chip on the board, the chippackage having the substrate 100 and the electronic device including thesame may be processed.

Referring to FIG. 38, on the upper surface of the substrate 100, thefirst inner lead pattern part I1, the second inner lead pattern part I2,and the third inner lead pattern part I3, which are one area of theconductive pattern part CP, may be exposed to an outside through a firstnon-providing area NPA1 of the protective layer 410.

The plating layer may be connected to a chip in a non-providing area ofthe protective layer. In addition, on the upper surface of the substrate100, the first outer lead pattern part O1, which may be one area of theconductive pattern part CP, may be exposed to the outside through athird non-providing area NPA3 of the protective layer 410.

The first inner lead pattern part I1 and the third inner lead patternpart I3 may be a conductive pattern part connected to a chip through afirst connecting part. Ends of the first inner lead pattern part I1 andthe third inner lead pattern part I3 may be provided in the same row.For example, a plurality of the first inner lead pattern parts I1 may bespaced apart from each other in a horizontal direction (x-axisdirection) of a substrate, and ends of the first inner lead pattern partI1 may be provided in a same row. For example, a plurality of the thirdinner lead pattern parts I3 may be spaced apart from each other in ahorizontal direction (x-axis direction) of a substrate, and the ends ofthe third inner lead pattern part I3 may be provided in the same row.Accordingly, the first inner lead pattern part I1 and the third innerlead pattern part I3 may be excellent in bonding with a first connectingpart and a driving chip.

A plurality of the second via holes V2 may be spaced apart from eachother in a horizontal direction (x-axis direction) of a substrate, andmay be provided in a same row. A plurality of the third via holes V3 maybe spaced apart from each other in a horizontal direction (x-axisdirection) of a substrate, and may be provided in the same row.

The end of the first inner lead pattern part I1 may be spaced apart froman end of a second inner lead pattern part I2. The second inner leadpattern part I2 may be a conductive pattern that may not be bonded to adriving chip. At least one end of one end and the other end of thesecond inner lead pattern part I2 may not be provided in the same row.

For example, a plurality of the second inner lead pattern parts I2 maybe spaced from each other in a horizontal direction (x-axis direction)of a substrate. A distance between at least one end of the one end andthe other end of the second inner lead pattern part I1 and the end ofthe first inner lead pattern part I1 may decrease as closer to thehorizontal direction (x-axis direction) of the substrate. A distancebetween at least one end of the one end and the other end of the secondinner lead pattern part I2 and the end of the first inner lead patternpart I1 may increase as closer to the horizontal direction (x-axisdirection) of the substrate. A plurality of the first via holes V1 maybe spaced apart from each other and provided in different rows in ahorizontal direction (x-axis direction) of a substrate.

The length between one end and the other end of the second inner leadpattern part I2 may include a first set part of the second inner leadpattern parts I2 gradually decreasing as closer to the horizontaldirection (x-axis direction) of the substrate. A length between one endand the other end of the second inner lead pattern part I2 may include afirst set part of the second inner lead pattern parts I2 that graduallydecreases from a first length to a second length as closer toward thehorizontal direction (x-axis direction) of the substrate. The firstlength may be larger than the second length. A plurality of first setsmay be provided on the substrate 100. Accordingly, on the substrate 100,the second inner lead pattern parts I2 may be gradually reduced inlength from the first length to the second length. The second inner leadpattern part I2 adjacent to the second inner lead pattern part I2 havingthe second length may have a first length again. Accordingly, a firstset part of the second inner lead pattern parts I2, whose length isgradually reduced from the first length to the second length as closerto a horizontal (x-axis direction) of the substrate; and the first setpart of the second inner lead pattern parts I2, whose length isgradually reduced from the first length to the second length, may berepeatedly provided.

A distance between at least one end of the one end and the other end ofthe second inner lead pattern part I1 and the end of the first innerlead pattern part I1 may decrease as closer to the horizontal direction(x-axis direction) of the substrate. A plurality of the first inner leadpattern parts I1 may be spaced apart from each other by a firstdistance. One end of the second inner lead pattern part I2 may belocated in an area between two adjacent first inner lead pattern partsI1 which may be spaced apart from each other. In a horizontal directionof the substrate, the end of the first inner lead pattern part I1 andthe end of the second inner lead pattern part I2 may be alternatelyprovided.

Referring to FIG. 39, on the lower surface of the substrate 100 of theembodiment, the fourth inner lead pattern part I4 and the fourth outerlead pattern part O4, which may be one area of the conductive patternpart CP, may be exposed to the outside through the third non-providingarea NPA3 of the protective layer 420.

FIG. 40 is a cross-sectional view of a pattern shape of a lead patternpart of an all-in-one chip on film (COF) flexible circuit boardaccording to an embodiment. In detail, FIG. 40 is a cross-sectional viewillustrating a cross sectional shape on one surface of the lead patternpart. The conductive pattern part may form a pattern by sequentiallyforming a seed metal layer and a conductive metal layer on a basesubstrate, then laminating a photoresist layer, and performing exposure,development, and etching. Thereafter, the seed metal layer may beremoved. The base substrate may be etched.

For example, when sputtering a seed metal layer on a base substrate, ashort circuit may occur as adjacent patterns are electrically connected.In order to solve this problem, one surface of the base substratelocated between the patterns may be etched. Thus, the seed layerinjected into the base substrate may be removed, and a short circuit ofadjacent patterns may be prevented. Therefore, the base substrate may beetched up to a predetermined depth for electrical isolation of adjacentpatterns.

Accordingly, the lead pattern part may include a wiring pattern layer200 and a plating layer 300 on a substrate 100. A thickness of asubstrate in an area in which a conductive pattern part CP is formed maybe larger than that of a substrate having no pattern.

Since the COF module is flexible, various electronic devices may beused. For example, referring to FIG. 41, the COF module may be includedin a flexible touch window. Accordingly, a touch device including theCOF module may be a flexible touch device. Thus, a user may fold or bendthe touch window or touch device. Such a flexible touch window may beapplied, for example, to a wearable touch device.

Referring to FIG. 42, the COF module may be included in various wearabletouch devices such as a curved display. The electronic device includingthe COF module may be thin or lightweight.

Referring to FIG. 43, the COF module may be applied in variouselectronic devices having a display portion, such as, e.g., a TV, amonitor, and a notebook. The COF module may also be applied in anelectronic device having a curved display portion. However, theembodiment is not limited thereto, and such a COF flexible circuit boardand a COF module obtained by processing the same may be applied invarious electronic devices.

In a flexible circuit board according to embodiments disclosed herein, awiring pattern layer may be provided on a substrate having a bendingarea and a non-bending area, and a plating layer having an open area maybe provided on the wiring pattern layer. A protective layer may contactone surface of the wiring pattern layer and a side surface of theplating layer exposed at the open area. The plating layer may include afirst plating layer and a second plating layer provided in two layers. Awidth of an open area of the second plating layer may be larger than awidth of an open area of the first plating layer. The protective layermay contact an upper surface of the first plating layer. As one surfaceof the protective layer contacts the first plating layer, a crackgenerated in the wiring pattern layer and/or the plating layer may beprevented at a portion with tension when the flexible circuit board anda chip on film (COF) module including the same are folded. Therefore,reliability of the flexible circuit board and the COF module includingthe same according to the embodiments may be improved.

In the flexible circuit board according to the embodiments disclosedherein, the protective layer may be provided of two layers. and theflexible circuit board may include an upper protective layer and a lowerprotective layer. The upper protective layer may have a larger widththan a width of the lower protective layer.

The upper protective layer may be provided to have a wider width thanthe lower protective layer, and stress due to tension or compression maybe dispersed, and damage due to deformation may be prevented. Therefore,reliability and lifetime of the flexible circuit board according to theexemplary embodiments may be improved.

The upper protective layer may cover the lower protective layer and asecond plating layer located in a peripheral part of the lowerprotective layer. Accordingly, it may be possible to prevent damageand/or removal of a film caused by oxidation of a wiring pattern due toinfiltration of moisture or foreign matter into an interface between thesecond plating layer and the lower protective layer.

An upper surface of the lower protective layer of the flexible circuitboard may be provided higher than an upper surface of the second platinglayer. And thus, it may be possible to prevent formation of a cavitypart between the lower protective layer and the plating layer or betweenthe lower protective layer and the wiring pattern layer. Accordingly,removal of a film or damage of the wiring pattern layer and/or theplating layer may be prevented.

A part of the lower protective layer of the flexible circuit board maybe in contact with an upper surface of the first plating layer. Thelower protective layer may be provided to cover an upper surface of thewiring pattern layer, a side surface of the first plating layer, and apart of the upper surface of the first plating layer. As the lowerprotective layer contacts the first plating layer, it may be possible toprevent a crack from being generated in the wiring pattern layer and/orthe plating layer at a portion with tension when the flexible circuitboard and the chip on film (COF) module including the same are folded.Therefore, reliability of the flexible circuit board and the COF moduleincluding the same according to the exemplary embodiments may beimproved.

In addition, by providing a plating layer partially on a wiring patternlayer, generation of metal particles, such as Sn particles, generated ina plating process may be reduced, thereby improving reliability of aflexible circuit board and a COF module including the same. As at leastone protective layer of a first protective layer and a second protectivelayer of a double-sided COF flexible circuit board may be in contactwith a wiring pattern layer, a crack due to a change in tensile forceduring bending may be prevented. Moreover, a semiconductor chip may bemounted in a narrow region of an electronic device in or with highdensity. Therefore, a high-resolution display may be realized.

According to embodiments disclosed herein, a flexible circuit board mayinclude: a substrate having a bending area and a non-bending area; awiring pattern layer provided on a bending area and a non-bending areaon the substrate; a plating layer provided on the wiring pattern layerand having an open area in an area corresponding to the bending area;and a protective layer directly contacting one surface of the wiringpattern layer exposed to the open area and a side surface of the platinglayer, wherein the protective layer is provided to have a largerthickness than that of the plating layer.

According to embodiments disclosed herein, a flexible circuit board mayinclude: a substrate having a bending area and a non-bending area; afirst wiring pattern layer provided on a bending area and a non-bendingarea on one surface of the substrate; a first plating layer provided onthe first wiring pattern layer and having an open area in an areacorresponding to the bending area; a second plating layer provided onthe first plating layer; a first protective layer directly contactingone surface of the first wiring pattern layer exposed at the open area,a side surface of the first plating layer, and a side surface of thesecond plating layer; a second wiring pattern layer provided on abending area and a non-bending area on the other surface opposite to theone surface of the substrate; a third plating layer provided on thesecond wiring pattern layer; a fourth plating layer provided on thethird plating layer; and a second protective layer provided on an areacorresponding to the bending area on the other surface of the substrate,wherein the first protective layer is provided higher than an uppersurface of the second plating layer.

According to embodiments disclosed herein, an electronic device mayinclude: a flexible circuit board having a wiring pattern layer on onesurface or both surfaces of a substrate; a display panel connected toone end of the flexible circuit board; and a printed circuit boardconnected to the other end opposite to the one end of the flexiblecircuit board.

Any reference in this specification to “one embodiment,” “anembodiment,” “example embodiment,” etc., means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention. Theappearances of such phrases in various places in the specification arenot necessarily all referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with any embodiment, it is submitted that it is within thepurview of one skilled in the art to effect such feature, structure, orcharacteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. More particularly, various variations and modificationsare possible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

What is claimed is:
 1. A flexible circuit board comprising: a substrate;a first wiring pattern layer provided on a first surface of thesubstrate; a first plating layer provided on the first wiring patternlayer and including a first open area; a second plating layer providedon the first plating layer and including a second open area; a firstprotective layer that directly contacts one surface of the first wiringpattern layer exposed at the first open area, a side surface of thefirst plating layer, and a side surface of the second plating layer; asecond wiring pattern layer provided under a second surface opposite tothe first surface of the substrate; a third plating layer provided underthe second wiring pattern layer; a fourth plating layer provided underthe third plating layer; and a second protective layer provided underthe fourth plating layer, wherein the first protective layer is providedhigher than an upper surface of the second plating layer, wherein awidth of the second open area of the second plating layer is larger thana width of the first open area of the first plating layer, and whereinan upper surface of the first plating layer exposed in the second openarea is in direct contact with the first protective layer.
 2. Theflexible circuit board of claim 1, wherein the substrate has a bendingarea and a non-bending area; wherein the first open area is an areacorresponding to the bending area; wherein the first wiring patternlayer is provided on the bending area and the non-bending area on thefirst surface of the substrate; and wherein the second protective layeris provided on an area corresponding to the bending area on the secondsurface of the substrate.
 3. The flexible circuit board of claim 2,wherein the third plating layer and the fourth plating layer include anopen area in an area corresponding to the bending area, and the secondprotective layer contacts one surface of the second wiring patternlayer.
 4. The flexible circuit board of claim 3, wherein an open area onthe first surface of the substrate vertically overlaps with an open areaon the second surface of the substrate.
 5. The flexible circuit board ofclaim 2, wherein an outer side of a first end of the bending areaincludes a first overlapping region in which the first plating layer andthe first protective layer are in contact with each other, and an outerside of a second end of the bending area includes a second overlappingregion in which the first plating layer and the first protective layerare in contact with each other.
 6. The flexible circuit board of claim5, wherein a width of the first overlapping region corresponds to or isdifferent from a width of the second overlapping region.
 7. The flexiblecircuit board of claim 1, wherein the first protective layer isoverlapped with the second protective layer in a vertical direction. 8.The flexible circuit board of claim 7, wherein a width of the firstprotective layer is equal to a width of the second protective layer. 9.The flexible circuit board of claim 1, wherein a width of a contact areabetween the first protective layer and the first wiring pattern layer isequal to a width of a contact area between the second protective layerand the second wiring pattern layer.
 10. The flexible circuit board ofclaim 1, wherein the first protective layer includes an upper firstprotective layer and a lower first protective layer disposed in twolayers.
 11. The flexible circuit board of claim 10, wherein the upperprotective layer has a larger width than that of the lower protectivelayer.
 12. The flexible circuit board of claim 1, wherein a thickness ofthe first protective layer is larger than a thickness of the secondprotective layer.
 13. The flexible circuit board of claim 1, wherein atleast one protective layer of the first protective layer and the secondprotective layer has a thickness of 1 to 20 μm.
 14. The flexible circuitboard of claim 1, wherein the second protective layer is in contact withone surface of the fourth plating layer.
 15. The flexible circuit boardof claim 1, wherein a cross-sectional shape of at least one protectivelayer of the first protective layer and the second protective layer isT-shaped.
 16. The flexible circuit board of claim 1, wherein the firstprotective layer has a shape different from a shape of the secondprotective layer.
 17. A flexible circuit board, comprising: a substrate;a first wiring pattern layer provided on a first surface of thesubstrate; a first plating layer provided on the first wiring patternlayer, and including a first open area; a second plating layer providedon the first plating layer; a first protective layer that directlycontacts one surface of the first wiring pattern layer exposed at thefirst open area, a side surface of the first plating layer, and a sidesurface of the second plating layer; a second wiring pattern layerprovided under a second surface opposite to the first surface of thesubstrate; a third plating layer provided under the second wiringpattern layer; a fourth plating layer provided under the third platinglayer; and a second protective layer provided under the fourth platinglayer, wherein the first protective layer is provided higher than anupper surface of the second plating layer, wherein the first protectivelayer includes an upper first protective layer and a lower firstprotective layer, and wherein the upper protective layer has a largerwidth than that of the lower protective layer.
 18. The flexible circuitboard of claim 17, wherein the substrate has a bending area and anon-bending area, wherein the first open area is an area correspondingto the bending area, wherein the first wiring pattern layer is providedon the bending area and the non-bending area on the first surface of thesubstrate, and wherein the second protective layer is provided on anarea corresponding to the bending area on the second surface of thesubstrate.
 19. The flexible circuit board of claim 17, wherein the upperfirst protective layer is provided higher than an upper surface of thesecond plating layer.
 20. The flexible circuit board of claim 17,wherein a width of a second open area of the second plating layer islarger than a width of the first open area of the first plating layer.